You can ask this about a lot of foods, but probably won't get many satisfying answers. For example cheese goes back many thousands of years, and it's theorized that it was invented accidentally due to storing milk in sheep stomachs or similar.
Probably something similar for pickling. Someone noticed that salted foods last a long time, and vinegar never seems to go bad, so why not try combining them?
What about hakarl? "Rotten" icelandic shark meat. It stinks to high heaven. Yet somebody thought "let's eat this". I can't imagine how hungry they must have been. And, if it doesn't decompose for 6 weeks under sand, it's toxic, so you die if you eat it. I'm sure they knew that. Yet they still tried it... Must've been a helluva famine.
> Yet they still tried it... Must've been a helluva famine.
Humans have lived at subsistence level, one bad harvest away from famine for most of history. Our modern abundance is very recent (1-3 generations) thing depending on where you were born.
So I think a tremendous amount of food discovery was a combination of food accidents didn't want food to go to waste, and desperation level eating anything to delay death from starvation.
Probably something similar for pickling. Someone noticed that salted foods last a long time, and vinegar never seems to go bad, so why not try combining them?