Was his dad with him? Maybe ds was referring to his dad?
But if not, then my vote is on being funny. I think you could "ask" him in a way. You can name things correctly and incorrectly and see what his reaction is. (Of course, if this tickles him, you might just start a trend where he does that all the time...)
I remember when dd was younger I took everything she did as equivocal (was that really a word? is she actually comprehending what that means, or is it just a loose association? etc., etc.) until the evidence was overwhelming.
Regardless of what he was doing, I can't see the downside to him laughing.
