What if the kid is listening to white noise to block out the sound of the coffee shop? Or the audiobook?
I'm not entirely sure it's even always true compared to silence. Sometimes I feel like other bits of my own brain can be competing for attention and that occupying them can be a win.
Dunno, however, if reading qualifies as such a task. Namely, the question is whether the same regions of the brain are engaged (and would be busy listening to music).