Question about lens hoods that I never thought about.

Having just acquired a 100-400 lens, the hood that came with it is called a bayonet, as opposed to a petal? Can someone help me with the terminology?

I read somewhere that with zoom lenses one would use a petal hood. Mine didn't come with a petal hood. And I saw someone the other day with what looked like my lens or maybe bigger, and maybe it was not a zoom but a fixed length with a petal hood.

Can someone help me with these questions? I have to say, the hood that came with this lens is quite big. And please excuse my ignorance on this subject. Still learning here.