Could be that either one of you had at that point a slow internet and could not transmit the game title from that person to server or from server to you.
Come to think of it, I've never seen it update when people play DS games -- could be because the feature is turned off because of the sandbox DS mode. DSi games could be in the same boat. This could mean that the only games you'll see people playing when they're online are 3DS games.