Well they use little bluetooth style earpieces all the time to talk to each other, but this one time he name-checks it very awkwardly. I think they just assume anybody listening would have to target their comms specifically, and most of the time they're relying on obscurity. I don't think it would make sense for most of their targets to listen out for every bluetooth dongle that enters the building or whatever.

They also don't have government resources so they have to make do with what they can get their hands on, which is a running theme. One of the times he's working for the government they specifically call out that his earpiece is so deep in his ear canal there's no way anybody will overhear what's being said to him.