Hmmmm...I'm not sure what could have caused it based on the pics. Everything looks good. The enclosure looks awesome, actually.
I still say you're playing with fire having the tape in there, though. Although it looks secure now, there's a reason it's strongly advised not to use tape in an enclosure. I've seen pics that are heartbreaking, and read some horror stories, including one that ended up fatal.
In my personal opinion, it's just not worth the risk.
In any case, it looks like it's superficial and nothing that will effect the snakes health. It will most likely be gone next shed.