So assuming everything the OP is true, it sounds like OP saved the map and loaded it in the Developer Package to look at how stuff was done. Got banned for "stealing the map and taking credit for it"?
Now under the above case, it's obvious he didn't steal the map. But is it true he was taking credit for it? Were other players on, were they playing rounds?
On another note, permanent is really harsh for a build steal. And quite honestly it's your fault for literally giving away your maps by hosting. If you don't want build stealers then don't host. HOWEVER, I would understand IF he was indeed taking credit for it. This honestly sounds like a misunderstanding.