While I have no comment about PMs, the "...just to annoy me..." appears incorrect.
If you don't mind me, giving an alternative version.
There is at least one post of 'his?', which seems to be a personal attack against Dave himself.
So, it does seem to be a 'throw away'/burner type of account.
But I could be wrong.
Also, the attacking post (and/or rather rude), seems weird, if the user has only recently joined the forum and got a small post count.
I.e. A real new user, is unlikely to attack Dave.