Either of them could have gone with the word. It was being able to determine that it was a code word in the first place that had Sam spitting it out. He had identified as such immediately and it made Sam wonder briefly if this really was as messed up as a situation as 'Dean' had painted it to be. had there really been an older version of himself here before this? Was he in the wrong timeline? Had some freaky sci-fi crap gone down? Something worse than what he was actually used to?
The man sort of looked like Dean. Or what Dean might look like if he had been older.
"Where does Dad keep track of all his hunts?" The answer was pretty simple. Their Dad kept a journal. It was a jumbled mess of notes, theories, and thoughts that John Winchester had jotted into all the time. Sam found it himself when he was a kid. He still snuck it away from Dad when he didn't think he noticed. "Tell me." He didn't lower the gun just yet, but the uncertainty on his face showed that he was definitely getting there.