Yes, you are right about what the NT says about the angels "in heaven", but these had left heaven willingly in order to do this wickedness. Lately, I have been reading and rereading these accounts and I continue to come to the same conclusions. Interestingly, after talking personally with various individuals, pastors and teachers, there are quite a few who believe this interpretation to be the accurate account, that it is referring to angels.

Hisalone
Matt. 6:33 But seek ye first the kingdom of God, and his righteousness; and all these things shall be added unto you. KJV