People don't stop being trans because you disagree with them politically. I despise Jenner and other high profile trans grifters but I'm not shitty enough to deny their identities.
Do better. As a user of both sites this shit is genuinely upsetting. Despite how you may feel about hexbear, how can you claim that they bait people into revealing their internalized transphobia and then turn around and make shitty claims like this? I don't give a shit if you call me a tankie or red fash or whatever, but I'm trans whether you like me or not.
I understand why you're upset and I agree this isn't okay. We can only know this little bit about people online and we have to trust that they are giving us that information in good faith - if they claim to be trans, we need to accept them as the trans person that they are.