Trish was the one with faith, not him. Cole didn't diss anyone for believing what they needed to to get through life, he was in no position to judge. He just didn't know and wasn't willing to commit himself to believing something he couldn't see real evidence of before him. When he died (or whenever it stuck, because he knew he should be dead), if there were pearly white gates surrounded by clouds and God walked out to say hello? He'd believe. Until that day, he was just going to live his life, try and do good with what power he'd been given, and hope for the best.
So no, he didn't believe that Cas was an angel. Teleporting? Normal conduits could do that. Super strength? Hell, he was already doing shit with his own body now that was on par with that sort of stuff. Nothing had proven that Cas was anything but a Human Plus or some kind of conduit who went a little God-crazy in the process.
Then the clouds began to gather and darken, the familiar charge of lightning forming above them. Cole kept his eyes intently on Castiel as they finally crackled and struck, the light casting a shadow of something he never would have expected to see. Still unsure and not content with just a flicker, Cole drew out both his arms and summoned forth more lightning, bright and as strong as could be, drawing it into himself and sending more light out to keep that shadow cast for as long as he needed to be sure of exactly what he was seeing.
As he felt himself overcharge, every bit of exhaustion from the trip dissipating, Cole was finally satisfied after a few long, studious moments. Once he released the lightning and let himself breath, Cole shook his head and said. "Right. Never seen anything like that before. I've seen some conduits become something completely inhuman, but if you had wings, they'd show up all the time, not like that." Casting a shadow like some kind of anima banner? That didn't make any kind of sense.