That means that if you’re in the fandom of Teenage Mutant Ninja Turtles, Sonic the Hedgehog, etc. You. Are. A. Furry.
technically, this isn’t exclusively true since most of the time the specific fandom actually supersedes the anthro aspect of it. For example if ur a sonic fandom nerd, you’re a sonic fandom nerd, but you may not have a general interest in anthropomorphic characters more broadly, in which case you wouldn’t be a furry. These things are not directly related.
The more correct definition here would be “a fan of anthropomorphic characters more broadly, specifically those within the furry community, and the furry community itself more broadly” It’s also worth noting that most of the time it’s actually done via self admittance. There are fursuit makers who do not consider themselves to be furries. It’s odd, but it’s how works.
Otherwise we start to define people who drive cars as “car people” and that’s just, wrong.
For example a lot of people have pets, dog/cat whatever, they talk to their pets, that’s literally anthropomorphizing an animal. Or personification, it’s the same shit at the end of the day though. Does that make those people furries? Because they speak to their dog in a language it doesn’t understand? Or apply human concepts to their pets that don’t really exist?