Tough spot. He's certainly entitled to ask you, although I think I'd prefer not to be asked to begin with, just like you. In a perfect world he should've just worn the eye shades. That's what they're for.

Were your windows the only ones open in the cabin? If not, then I think it's a bizarre request. Because I find in the F cabin, it really doesn't make a difference if the person in front/behind has 2 or 3 windows open - it's kinda the same. The light reflects much more off the ceiling. Same thing if you're in say 1A, if the guy in 1K has all his windows open you're still going to notice it even in 1A, because it reflects around inside the cabin and throw that window in the D seat. As for the person sitting behind you, their window light doesn't really penetrate the side of the seat, unless maybe the sun was at such an angle that it was somehow reflecting into the front of his seat?