Do you have any screenshots for this?
It's not the first time that someone has received a PM of this format that tried to phish people into entering their forum usernames and passwords. I've received one of those PMs as well, from someone that I didn't know.
I don't think that the person that sent you the PM who is also affiliated with sportsbet.io intentionally did it. Most likely, his account was hacked as well due to his password being leaked, perhaps phished in the same way. Just don't click on the link, and let him know. But you're right, I think sportsbet.io has had some pretty shady dealings in the past, which resulted in their reputation being tainted:
https://bitcointalk.org/index.php?action=trust;u=832366