When Cas caught sight of the other man following Piotr's lead, it was unintentional. His eyes had merely fallen upon him, but there was something familiar within him, something...
Oh.
Oh.
The realization was abrupt, but it was similar to what he'd sensed before on the cruise liner anytime he'd come into close contact with either of Sam and Jo's offspring. Immediately, several thoughts began racing through his mind. Was Dean aware? Was Jo? Or perhaps the boy himself was not aware - to say anything would be to compromise a family, but the fact that he could sense some essence of Sam Winchester as plainly as he ever could in the past was both fascinating and disconcerting.
He...he needed a drink. Or to kill something. Or...to perhaps just discuss it with Anna later or perhaps Mary. At the moment, he needed to focus on the alien.