It was definitely a grief trap if;
A) You were banned Immediately.
Usually if your online and you griefed something a Mod will give you the chance to explain yourself before simply banning you. That said, my question is why didn't you dig down and off to the side when you saw you were digging up into something? Automatic Grief Farms don't ban you after breaking one or two blocks. They give you a chance to go "oh crap" and stop what you're doing. You actually have to break quite a bit before it bans you.
Automated grief bans are 7 days and due to the facts I just stated they can't be lifted, so if that's the case you'll have to wait.
I can't get in-game right now to be sure it was an auto-ban, so please wait for another mod to post the details.