Hi, I'm not really a user here, I forgot why I even registered here a while back.
I use a specific email for sketchUcation (just fyi you can do this easily with gmail by using username+anythingyouwant@gmail.com), and despite not using it anywhere else, I just received an email to it. I don't use the gmail trick to be clear, the email I used is specifically sketchucation@mydomain.tld. The spam email I received was from igorproxorov96 at gmail.com containing "Sketchucation, hello, is it your email?"
Based on that, I can only conclude a part of the database was leaked or there was a access breach. The latter is most likely if phpBB is out of date.
I recommend you change your password at the very least and use a password manager so you don't reuse passwords on other websites as well.
Anyways, uh, good luck with that.