"Trials--?" Castiel narrowed his eyes again, and thought on that for a moment. "From the tablet. The Demon tablet." He remembered that. Although when it had last been brought up to him he hadn't exactly been in the right frame of mind to fully care. Not to put too fine a line on it, he'd been out of his mind -- but that had been the least he could do. For Sam. To take his hallucinations, since Castiel had been the one to break his walls in the first place.
He nodded then, and then opened the door of the diner, allowing Sam to go in before him. "You're from my future, I think. I -- was in Purgatory." Which still didn't explain how he ended up here, but weird things happened all the time and he found he wasn't as concerned over it as he should have been. It was hard to be upset about being in fake Nevada when he wasn't currently being hunted by anything. Having the Winchesters near helped too, even if he was aware he didn't really deserve that comfort.
"You're right. There's something off about you. I don't think I'll be able to fix it. Not fully. But maybe." He couldn't yet, he just wasn't strong enough. But soon. Soon he'd try.