I suppose that's possible but how often do you see people get up before the aircraft has slowed to 10-15 MPH...that is,when it's within feet of the gate? I've never done it and I've never seen it and I've done a fair amount of flying in my day.
I fly regularly and I have see someone do this only once, and it was a dash to the lavatory. We stayed put on the taxiway 'till the lady got back to her seat.
I do see it, more so in economy than in First Class, but still.
Wowzer, I have seen someone get up and sprint up the aisle to the restroom and the flight attendants just glare b/c they are not going to get up at that point and chase the person.
Also there are many airports with a fairly long taxi to the gate after landing. Some even have intersections where a taxiing plane has to wait. So, yes, people do get up, even though the seatbelt light is still on.
I also see people unbuckle at this point and not get up, but sort of get up and tug on, say, a jacket in the overhead or lean over and get stuff from under the seat in front of them.
Again, not saying any of this applies to Mays, just that it’s possible.