That's quite the start to this fight; a throw that THE Yamashita Kazuo couldn't see.
I doubt the earbuds are anyone giving him instructions; after all, whoever might have been talking would have noted he had taken them out at the start and it would have been useless to say anything else whereas there is sound coming out of the earbuds at then end of the chapter.
I also doubt the earbuds were keeping him in check or anything. I mean, I would have to go back but I don't think he was wearing them at all times so I don't see him as needing them for anything.
What we should note is that he forgot they were there even though they were still clearly working and that he seemed to hear perfectly fine even despite wearing them (and I'm not saying you can't hear over earbuds, especially if they don't fit well). So he can tune out certain sounds and hears well?
Or perhaps he just enjoys a good beat and it gets him in the rhythm.
Meanwhile we don't know what's up with Raian, Kiryu and Ryuki, and Muteba but those are three story threads that were initiated and for which we should eventually get an update.