I'm participating — well, mostly lurking — in a therian forum and often see long-time members talk about how the community has changed. One of the earlier phenomenons was "grilling", i.e. asking newcomers invasive questions to make sure they were genuine. This practice had died by the time I learned about therians, thankfully, but it certainly was a thing when that comic was released.
After the grilling, there was still a baseline of shared experiences you were expected to have. That's when I found therians and concluded I didn't fit because I didn't experience any of those "shifts" or animal instincts or some kind of awakening. To be extra clear, I know not all of these are required simultaneously, but I had nothing.
Nowadays, however, even that baseline has pretty much disappeared. If you want to be an animal — even if "only" anthropomorphic — , you can pick up the therian label and you're good to go. It couldn't be any less strict.