It looks like it's time to for some clarification about Operations Over People (OOP).
First, there is a legal way to fly over people currently. But unless this person had a waiver to do so, he was illegal. And since he has a
Mavic Air 2, he did not have a 107.39 Waiver because none have been granted but
Mavic Air 2 drones.
The only way to currently fly over people is with a drone that weighs less than 250g (or .55lbs), and has no "rotating parts that will lacerate human skin" upon contact. This describes Category 1 OOP compliant drones only. The official definition of 14 CFR § 107.110 can be found on page 4383 here:
https://www.govinfo.gov/content/pkg/FR-2021-01-15/pdf/2020-28947.pdf. The FAA does not certify Category 1 drone, it is up to the Remote Pilot in Command to do so.
Also, there are no Category 2-4 drones out yet.
OOP is only available to people who have a current Remote Pilot Certificate are flying under Part 107 rules. TRUST has nothing to do with it, and recreational flyers are not allowed to fly their drones over people regardless of permissions asked and/or granted by those being flown over.
Even if this guy had a 107.110 compliant drone, he would only be allowed to fly over "open-air assemblies" if his drone had Remote ID (RID) capabilities as described in either § 89.110 or § 89.115(a). And since RID doesn't exist yet, that's not an option. So yes, this guy was 100% illegal in his flight. There is no way for him to be compliant with any of the current legal options for OOP.
So before I am asked how I would have handled it, I would have approached him and advised him to land as soon as safely possible. I would have helped him clear a spot to land. And then I would have taken that opportunity to educate him on safe a responsible drone use.
The FAA asked us to self-police whenever possible. This would have been a perfect chance to do that. And since he was flying in such a fashion, it's a safe bet he wasn't registered as a Recreational Flyer, have TRUST under his belt (& have a copy with him), or have his registration number on his drone.
It's up to all of us to keep this industry and hobby safe. This would have been a perfect chance to do that.