sbm, in the situation that you describe it sounds like the if the pair travelling together is say a mother and her minor child (you mentioned one of them was a minor, right), it sounds perfectly reasonable that CO should rearrange people if necessary to ensure that they sit together. Obviously shouldn't have moved them to an exit row, but it's understandable that exceptions are made for folks in that situation.
I agree that folks should be moved about to accommodate others as necessary, but I also think that CO should actually tell passengers that rather than lie to them. And the pair traveling together should've been given the worse seats, not the better ones, but that's a whole different story.
Like I said above, there is a history in the reservation that would explain exactly who moved
craz out of his seat and probably why. Sadly CO doesn't want to share that information ever.