What caused this weird burn? (Pics)

Could be humidity but I don't think so.

Judging by the uniformity of the remainder of the stick I would say the RH is good, if it was high typically you would see swelling while smoking it as the excess humidity is forced back in the stick from the heat.

I would say you got a bad roll, an air pocket or a piece of stem. Looks like it was getting over smoked too but that is only my guess, slow down............enjoy and rotate the stick as you smoke it.