How is this of your concern?
I am not seeing how this can bother you.
Some players want to get into the end game and not being bothered by leveling. May they did level 7 or 8 chars already.
I can understand that at that point you wanna skip leveling.
So you saw him in-game and you took it upon yourself to be rude and criticize how he spends HIS money? How does the fact that he spends HIS money on a 85 to 90 character boost affect your gameplay in any way? I really have a hard time understanding why you're actually complaining. It's his time and his money, it's got nothing to do with you.