Charitably, could be an attention issue. I’ve had to start learning about ADHD as I’m basically the only one in my nuclear family without it, and a common thing is needing to be doing something while listening.
It is mildly infuriating at the best of times to have someone constantly fidget and squirm and not acknowledge you while you talk, but listening doesn’t always look like listening unfortunately.
Though, I haven’t heard of this specific thing while at a concert it’s not beyond imagining that it’s just a tactic to accommodate their own needs.