My eyes are highly light sensitive due to prism in the lenses because one of my eyes has muscular issues. So for me, I can understand the problem the guy was having, but not necessarily his actions.
An adult shouldn't be arguing with a kid, you discuss it with the parent
He changed his seat, so he really has no say. But if the light was in his eyes in his original seat, my vote would go to him
That being said, I preferred when it was business class, and no kids were allowed. I hate having to deal with parents and kids which is one of the reasons I spend extra on first class tickets.
Years ago I was on a flight in first, and they had everyone shut the blinds so people could watch the movie. As I said earlier, I have vision problems, and a bright light coming into a dark room can be painful for me.
There was a mother with a 2 or 3 year old kid a row behind me. I was in the middle section, they were in the window section the movie started, and about a half hour into it, the kid opens the shade. The mother reaches over and closes it, and is like No, Johnny, you shouldn't do that.
The kid, being 2 or 3, does what a kid that age does, and opens it again. The mother again, calmly tells him he shouldn't. This goes on 4 or 5 times, and it's apparent that the kid thinks it's a game.
I'm pretty much getting a migraine from the opening and closing, and am no longer even trying to watch the movie, but am now watching him waiting for him to open it again. When I see him reach for it, I gruffly look at him and say NO!.. The kid stops, and understands not to do it.
The mother on the other hand starts yelling at me for reprimanding her kid. I respond someone has to. The father, who was apparently in the row behind her tells her to calm down . She snarls at him. The shade stays down the rest of the flight.
I was on a flight a year or so ago, where the parents left their kids in Delta One, so they could theoretically sleep, and the parents sat elsewhere.
Fortunately I was on the other side of the plane, but the two kids were jumping around, throwing food and other things at each other and the FAs couldn't get the parents to do anything, as far as they were concerned, it was the FA's problem.
So bottom line, the plane isn't a kids playground,, and he had the right to ask you to shut it if he was being blinded by the light, but should not have engaged with a child