it's weird bitcointalk bother to send PM only for removed post.
My guess is it's a database thing: Deleting one post requires only 1 PM. Deleting one topic can require thousands of PMs.
I just checked modlog and found this.
Looks like the thread is deleted by moderator, but there's bug on forum automated PM.
When a thread is "deleted" it is actually moved to another sub, the
trashcan. The OP (and everyone else who is not forum staff) does not have permission to view threads in
trashcan, so they are unable to see the thread in their post history (the same with anyone who has posted in that thread), and their post count will not reflect posts in the thread.