"Winchester," Castiel confirmed. He assumed, naturally, that all angels knew the Winchester name, and didn't bother to elaborate. He raised his eyebrows. "There is more than one demon with the name Crowley? I find that highly unlikely." Like angels, demons could be summoned by name, and tended to associate a certain identity with the individuality. It wasn't like humans, where there could be several hundred Marys in any given area.
Castiel looked down at the hand, and then took his time as the vivid blue eyes came back up to meet Aziraphale's. He had not heard the name, which implied this angel was not especially significant on the universal scale. Castiel was polite, however. He took the hand and mimicked Dean Winchester's tendency for a firm shake, perhaps too firm, though he was not overzealous. He took his hand back. "I am Castiel." He didn't think Aziraphale would necessarily know him either, unless he took a special interest in the apocalyptic destiny of the Winchesters beyond your usual "they're gonna do it."