User blog comment:Epakrios/Plot holes/@comment-98.198.247.12-20140121083911/@comment-11331875-20140121222952

Hmm, I suppose that that could've been a hyperbole. Castiel had just realized that the angel in front of him was the one everyone said was responsible for all the demons and evil in Creation (which I would count as another overexaggeration--how exactly was he supposed to stop Lucifer, an archangel, even if he knew that Lucifer was up to no good? He didn't start all of it, Lucifer did), and he was obviously in a state of extremely high anger and hatred--he was about to attack Gadreel-in-Sam, one of his only friends, in front of Dean, his best friend. Guy wasn't thinking clearly. On the other hand, it's also possible that they're retconned evolution out of show mythology and now we're operating purely on Bible lore, complete with Adam and Eve being created right after the universe was made.

Keep in mind that it's been millions of years since Gadreel was locked away. Gadreel was seen as a failure and an embarrassment, to be stuck in the deepest, darkest part of Heaven's dungeon and never mentioned or thought of again; he hasn't seen or spoken to anyone besides prison guards the whole time. Unless he and Castiel were very good friends who regularly saw and interacted with each other (which doesn't seem to be the case), it's understandable that he wouldn't immediately recognize him. Hell, even then he might not recognize him. (Also keep in mind that Lucifer, who was locked away at around the same time Gadreel was, didn't seem to fully recognize Castiel when they met and had to ask to make sure what his name was.)

My plothole is why Castiel didn't realize that there was an angel in Sam in the first place; he recognized Ephraim as soon as he looked at him and Anna could sense angelic presences coming for her even when they weren't in the room. There's never been any indication that an angel can hide his presence inside a host from another angel. And if that's what Gadreel did, then it was sloppy story-telling not to bring it up and resolve it on-screen. It could've been as easy as Dean asking Gad why Castiel didn't notice him, and Gadreel saying that so long as Sam is in control and Gad hides himself deeply enough inside Sam, then no angels can detect him. Or something.