It’s best not to overthink it, as it seems you are doing (no offense meant).
If someone says ‘a’ is true, you can ask them how do you know ‘a’ is true, and if they just say oh because I know, then you can push further because that’s just a bullshit answer. Especially so if you take the comment in relation to the whole conversation you’re having with them, and the level of intellectual honesty they have in conversing with you.
As far as conversations go here on Lemmy, I’m not finding good quality of conversation here on Lemmy at all, and I’m seriously considering leaving and going back to Reddit because of that, unfortunately.
From the quality of new posts people are making to the arguments that end up happening right away inside of each one of them, it actually seems a lot worse than it was on Reddit. Good to hear it’s working out well for you though.