Nulled scripts are, in short, illegal versions of paid software. They're illegal because they've been edited by groups OTHER than the real developers to make them free, because someone felt paying the developers the $ they were entitled to was bad.
In your case, you shorted the developers of vBulletin at least $150 in license cash.
It's fairly easy to tell a nulled script as well. If you just got it for free and it costs money, it's nulled. Especially if it comes with a key generator, like yours.
As for the suspension, it's permanent and not able to be removed because a quick perusal of the files turned it up in a hurry - it's not a false positive suspension.