Dean might have used the same word, if he'd been pressed to describe Cas' sexuality, though it wasn't something that he cared to think about much. Cas' sexuality was Cas' sexuality. Dean had mostly given up on trying to exert any proactive influence upon that since Chastity, though obviously there had been some subconscious influence with the whole 'do whatever feels good and gets your mind of the bad' thing, in general. Dean preferred women, for sex, but when it came to booze, anything with alcohol would do. Maybe Cas really didn't have a preference yet, so anybody willing would do to give that mutual high. If you wanted it bad enough, a blowjob probably felt good, no matter whose mouth was performing the task.
But Dean wasn't sure he'd be able to explain it out loud, or what that might mean--so he shrugged again, and pulled the e-brake on that train of thought, right there.