Not in this case no, but even in the case where they were asked to stay late I would still find the idea that they had special priviledges to reconfigure their schedule unfair. As a parent myself I just believe I'm not entitled to special treatment at work because of the life choices I've made to have kids.
Was there complete transparency on salary there? I mean - that person might have made a deal with your employer to take a lower salary in return for that privilege. Either explicitly or simply by not getting the same raise as they would otherwise. I find it a bit peculiar that people concern themselves with these things, but have no problem with differential in pay.
