You need to understand how often people ask questions that seem to come from a place of ignorance but genuine curiosity and then take that discussion to tell trans folks that they are wrong. It happens so much that it’s the main way that transphobes try to infiltrate spaces meant for trans folks.
My honest response is to check that website out. If you are asking about this in trans spaces, bring zero opinions to the table and accept what is said back to you without debate. Debating trans folks’ existence is something that is forced upon them in their own spaces by malicious people asking and framing questions just like you’ve described.
It’s hard to take the “enlightened centrism” stance seriously when I see it used as an excuse. So many centrists tell trans folks that their identity is wrong and that they are mentally ill or chose this “lifestyle”. As if they want to be trans. As if they like feeling scared and being told they’re wrong about something as fundamental as their identity.