He could have:
* scrubbed the audio
* removed the section including the musical work
* overlaid a royalty free musical work to replace the copyrighted one
* asked the market vendor to turn the radio off
* waited until the radio played a work that was not copyrighted
* etc etc
He’s chosen to include copyrighted material in his content by not doing any of that. Some of which would have been relatively simple to do.
In court I would think it would be difficult to prove there was nothing he could have done to remove the offending audio.
And he also falls foul of Fair Use (there’s another comment somewhere that digs into the definitions of educational content in this case) as this is not incidental usage.
If he falls foul of Fair Use, then regular copyright laws come in to play, which takes the simplistic binary viewpoints:
* Is there copyrighted music or not?
* Is money being made from the use of music or not?
Yes to both => remunerate rights holders.