My guess is that early man also acted as a scavenger, eating freshly dead (or not so freshly dead! ewww) animals; maybe those things killed in forest or prairie fires lead them to think about using fire (once it was “domesticated”, what’s the word I’m looking for??) to cook what they caught/found.
…it has never been my way to bother much about things which you can’t cure.
A Connecticut Yankee in King Arthur’s Court-Mark Twain
I doubt primitive humans had very sophisticate palates. They ate whatever they could to stay alive. Plants are easy to obtain, so they get eaten first. When plant life becomes scarce, you start looking for alternate sources, likely freshly dead animals. That helps you develop a taste for meat, so you start thinking, “Hey, if I make that animal dead, I can eat it!”
As to how we learned what tasted good how, it was probably a long, long development. Early man ate raw and barely cooked meals because (a) he didn’t know better, and (b) didn’t have time to prepare them. As civilization developed, mankind had time to work with foodstuffs. Primitive recipes were developed by trial and error. When one technique (say, boiling) was found to work on one foodstuff, it may have been tried on others to see how they tasted.
“Sherlock Holmes once said that once you have eliminated the
impossible, whatever remains, however improbable, must be
the answer. I, however, do not like to eliminate the impossible.
The impossible often has a kind of integrity to it that the merely improbable lacks.”
– Douglas Adams’s Dirk Gently, Holistic Detective