Pasting links, especially to other BitcoinTalk threads, can trigger it.
The reason the topic was deleted is actually not because of links (if you check the archive, there is no single link). It was probably deleted because a low value topic or it had AI content as already stated by some member
I don't think it happens when the thread is moved to another board.
It can happen, especially if the board the topic has been moved is off limits is to certain ranks
For example, Investigations board is off limits to Newbie accounts