No flights of angels here.
Castiel doesn't have wings. Not really. Not in his true form. But an angel's human vessel cannot adequately contain all of their grace and so it occasionally manifests itself as the shadow of huge wings, extending out from the back of their vessel.
However, humans who have seen this have come to believe that angels truly do have wings, upon which they can take flight.
In actuality, Castiel moves between Heaven and Hell, points on Earth and in time with but a thought; taking anyone he chooses with him.
This would be a disappointing explanation for Dean though, Castiel can see it in his eyes. Dean needs to believe in something wonderful, to counterbalance all the evil he's seen in his short life.
So when Dean comments on how "frickin' awesome" it must be, to have two "huge, giant-ass wings" upon which he can "zoom through the sky", and also possibly use to "take out demons by flinging them out in a slicing style" which Dean then proceeds to demonstrate in his enthusiasm, leaning forward and then punching out his arms sideways; Castiel finds he cannot tell Dean the truth.
So, as is his custom when he cannot find the words to say, he just looks at Dean, and looks and looks and looks.
And Dean changes the subject.