I've seen this more in people seeing a private plurk than a PM to a journal. One person on my timeline at the time and a bunch of their friends conversing about how they get a shot of adrenaline even just seeing that they've had a private plurk because apparently they've been bullied in the past or confronted about behaviour that they didn't know was wrong.

So it's probably more of that then being surprised by someone wanting to RP with them.