Yeah, no, the slightest possibility of that being a joke or insult went whooshing right past him. Would have normally, even, not just while he's too cold to think.

He doesn't question being led into a black van by a stranger, either (someone get this kid some self preservation skills!). He fell in a lake, this man helped him, and he's apparently going to get answers and not freeze to death. It's all very strange and frightening, but in the absence of evidence to the contrary, he assumes Topher is trustworthy.

"Rec-cognized me?" he asked, not so out of it that he doesn't find that strange. "You know S-Sarah Jane?"