I've been thinking... would not be a good idea to somehow "force" all users to change their pass?
Terrible idea in my opinion when there's no good evidence of a security and/or database breach and leak of data. Well, it doesn't hurt to change your password and if you feel safer to do it, then do it. But forcing everybody without strong reasons? No thank you!
I'm quite confident that theymos spent considerable time to investigate if a breach could've happened. From his wording, I'd say, chances for a breach were not likely to have happened. I assume the forum server(s) log one-way to a separate log collecting server which isn't exposed to the internet and isn't likely to become compromised should a hacker manage to compromise the forum's webserver(s). It should not be possible to tamper the logs (in an ideal world).
I've a complex and unique password generated by my password manager, 2FA is enabled here. I will have a closer look at the IP logs of my account in the next days and weeks and that's it. I could change my password, but I don't really feel the need to do it. YMMV!
Other services have already activated this type of feature after security breaches.
Makes sense after a security breach
is confirmed.