They probably encountered cooked meat after a forest fire and tried to replicate it. A pig that died hiding in a burning log, cooked low and slow for hours, is basically barbecue.

Whoever discovered cheese:

• Damn, my milk spoiled
• I’ll leave it out a bit longer maybe it fixes itself
• It’s better now!

More like random forest fire makes animals crispy. Caveman smells something weird. Finds an already cooked meal. It tastes better than their regular food. Starts burning everything and tasting it.