If the diaper just had pee in it I think the other people maybe should be understanding (probably not). If it had poop in it, it was pretty rude to change the kid on an eating tray, particularly one that is right next to stranger. Of course, you do what you gotta do. But when you don't gotta, you don't. And I think it's usually pretty unlikely that you have to change your kid there at that very moment or something very bad would happen or something. Waiting for six people for the restroom doesn't take that long. I think rather than doing what you gotta do, you did was was very convenient for you. In any case, I think handling bodily excretions on a shared eating surface isn't very classy or considerate. I mean, even just going to the back of the plane and changing the kid outside of the bathroom would be a better option.
And I have a child.