Spammers can and will obtain lists of people to send their messages to. Some will target forums members email lists, others buy them from semi legitimate sources. these are made up from members list from some sites that sell their memberships lists(expired memberships or query lists) on to businesses that acquire and sell email addies.
Another method they use is to run a program which will generate email addies, they bulk mail to them and look for replies, especially unsubscribe requests. ot shows that the email that replied is active and they will then place this addy onto an"active" list they will either target or sell on to other spammers and bulk mailers.
Saying the spam you received is directly as a result of the hacking on this site cannot be proven. Unless of course the email you used on this site was only used for this site and no other. And the spam was addresed to that specific email address. Check the address it was sent to if that is the case, and if it is a non generic type email addy(
me2@hotmail.co.uk as oppsed to
me2@aname.fsent.co.uk).
You could also look at the source of the email and run a trace back then complain to the originating source ISP.