Humans and our cattle are something like 95% of all land mammals, maybe they're thinking of that.

"Land vertebrates", #1 is chickens, #2 is humans. But colloquially "animal" does not include ants or fish.

Insects I'll consider fair enough, but fish? Are you leaning on "fish isn't meat"? Otherwise, this isn't a colloquial use I'm familiar with.

Just try referring to a fish, alive or dead or cooked, as an 'animal' to your friends. Even if it doesn't sound weird to you, your friends will feel misled in the conversation, even though it's technically/scientifically correct.

In terms of biomass humans are much larger than ants.