Not necessarily.
He might have been carrying his ipod with recorder attachment and punched record. Wouldn't be that hard to do with two yelling people fully absorbed in their own thing.
D
You can't make the assumption that it was an iPod either. My MP3 player is an RCA Lyra, which includes a 1 button voice recorder and a radio tuner. They're cheaper than iPods, and can be purchased in just about as many places.
There are a LOT of lower cost MP3 players on the market that include voice recording capability. This kid may have simply had one in his pocket (my teenage daughter can't be separated from her MP3 player nowadays) when he realized that the situation was getting a bit hairy.