What the hell, I guess he was trying to line it up? Some barbers love that and do it on even Norwood 0s and it looks bad once it grows out, you'll have to wait it out a few months or buzz your hair which you were planning for a bit. Or did he see some asymmetry and thought he would clean it up? One thing is lining up the temple triangles (peaks) but the hairline itself is annoying especially when a surgeon measured it and designed it to be good! Guess it was over before you knew it, but I would go back to him and tell him next time so he doesn't repeat it and switch barber as well.
I had a barber do this behind my ear lol, like he cut in too much last year and a week later it looked like crap. So I had to either keep lining it myself or let it grow and blend after a month - I did the latter, back and sides blend quicker as less length.