You are correct. All of AIbotBTC user's posts were in one single topic, the topic was moved to Trashcan. And since Trashcan is not available to ordinary users, then, accordingly, all his posts are not visible to the ordinary user, but they are displayed in the user's profile, as they have not been completely removed from the forum.
So let me see if I understand this right: so if a user's posts arrive, for some reasons, in Trashcan (either after having posts reported or if mods themselves decide to move the posts there), they still appear on user's profile but are not accessible anymore by regular users, right?
Yes, that's right.
If it is so, then why are some posts just moved there and not also deleted for good...? As far as I understand, this Trashcan acts like Windows' Recycle Bin. Are the posts supposed to be kept there for a certain amount of time...? Or some are not deleted at all and being kept as maybe they will be useful in the future, for some reasons...?
For one reason or another, moderators may delete the topic immediately or move it to trashcan. In this case, the moderators act at their discretion. Plus, moving a topic to trashcan allows global moderators to restore that topic at any time. If a moderator deletes the topic, they will have to contact theymos to restore it, only he can restore the topic in that case if needed.
I can't say for sure, but I think Trashcan is cleaned manually.