It seems that Chow-chow does not always refer to pickle. A couple of nineteenth century travelers had a very different perspective.
From The Stranger in China: Or, The Fan-qui's Visit to the Celestial Empire in 1836-7:
Chow-chow is another favourite word with the Chinese. When applied to little dogs and tender rats, and other delicate articles of food, it is spoken with great gusto. Where the river is troubled in particular parts near the shores by small eddies, that part of it is called chow-chow water. Baskets, which are procured in Canton, with many compartments, are called chow-chow baskets, while a mixture of different pickles or preserves bears the same alluring title of chow-chow. No doubt the Chinese, when they use these words, have a particular expression of countenance and of emphasis, to suit each idea; but as this is not perceptible when they talk to a stranger, he is apt to be in doubt what is meant, and he discovers that it is owing to the great scarcity of words in the Chinese language.
And from Travels in China, New Zealand, New South Wales, Van Diemen's Land, Cape Horn, (1840):
Monday, November 1. After breakfast I returned to Canton with Captain Neish, the Rev. Mr. Abeele, and Mr. Rayne. I found everything going on as formerly, the guns as well as the seamen, having been sent back to the ships at Whampoa. I accompanied Captain Morgan to the wharf, where the Chinese vessel was taking on board his Chow-chow Chop. The word Chow-chow signifies "eating," and the term Chow-chow Chop is consequently applied to the last chop-boat that is loaded for any ship, and which is supposed to carry all the private stores for the captain, officers, and crew.
I guess the question now is, at what point in Western cuisine did chow-chow become a pickle?
Here are two versions from What Mrs. Fisher Knows About Old Southern Cooking, (1881) by Abby Fisher.
Take one cabbage, a large one, and cut up fine. Put in a large jar or keg, and sprinkle over it thickly one pint of coarse salt. Let it remain in salt twelve hours, then scald the cut-up cabbage with one gallon of boiling vinegar. Cut up two gallons of cucumbers, green or pickled, and add to it; cut in pieces the size of the end of little finger. Then chop very fine two gallons more of cucumbers or pickles and add to the above. Seasonings: One pound of brown sugar, one tablespoonful of cayenne pepper, one tablespoonful of black pepper, two gallons of pure wine vinegar, two tablespoonfuls of tumerick, six onions, chopped fine or grated. Then put it on to cook in a large porcelain kettle, with a slow fire, for twelve hours. Stir it occasionally to keep it from burning. You can add more pepper than is here given if you like it hot.
Creole Chow Chow.
One gallon of green tomatoes, sliced thin, half dozen silver skin onions;sliced thin, one gallon wine vinegar, two tea-cups of brown sugar, one tablespoonful of cayenne pepper, one tablespoonful black pepper, one tablespoonful of tumerick. Put the onions and tomatoes together in a keg or jar and sprinkle over them one pint of salt and let it so remain twenty-four hours, then drain all the brine off from them over cullender, then put the vinegar to them and add the seasoning, and put to cook on a slow fire, stir to keep from burning. It will take the whole day to cook; you can make any quantity you want, by doubling the quantity of vegetables and seasonings here prescribed, or if you want a less quantity, lessen the proportion, say half the quantity, then you want a half gallon of tomatoes to begin with, and a half of everything else needed in this chow chow.
Jennie June's American Cookery Book (1866) gives three recipes for Chow-Chow, including this one:
Chop together very finely a head of cabbage, six green peppers, six green tomatoes, add two tea-spoonsful of mustard, sufficient salt, vinegar to wet it, and if desired a little cloves and allspice. It is ready then for use, and will keep a long time. No better appetizer can be made.
And here is another with onions and cauliflower, from the San Rafael Cook Book (1898)
12 large cucumbers, 4 large or 8 medium onions, 2 heads cauliflower, ½ peck green tomatoes cut in small pieces, 1 quart string beans (white wax beans are best) - string as for cooking, and break once; 3 large red peppers cut in strips, 50 small cucumbers about 2 inches long used whole, 2 quarts small silver onions, peeled and used whole. Pack all down in salt overnight. In the morning wash off the salt, and drain well in a colander. Then boil in 1 ½ gallons of good cider vinegar, adding 1 pound brown sugar. 2 ounces white mustard, 1 ounce celery seed whole. Into 1 pint cold vinegar thoroughly mix 1 small box yellow ground mustard, 4 tablespoons ground black pepper, 1 horseradish root grated, and 2 ounces turmeric; add to the boiling liquid, and boil all together from 2 ½ to 3 hours. Put into glass or stone jars, while still warm.
Another question, for another day, is – how does Chow-Chow differ from Piccalilli?