Regarding the first cite, my experience contradicts this. As with so many other things that have happened, this was unexpected. My thinking on this was identical to yours, that it was inconceivable to NOT have a trans identity. It is conceivable and apparently for others as well, the reality.
I hear things that stretch my credibility, too. Sometimes it's hard to find the line that separates truth from projection. I once disbelieved many things that I now know to be true. I wish I could say that I arrived at that point through some combination of external evidence and empathy, but not so.
I'm gaining a new appreciation of the post-ops's plight ... the utter lack of credibility with those who solicit their views and advice.