It may not be in that particular sentence since he's directing that "A+" label towards the candidates. (He's being genuinely charitable towards the job seekers.) However, when he's directing the "A+" label towards the interviewing team, it comes across as a backhanded swipe.

Perhaps calling it "sarcasm" is too strong since his sarcasm is very subtle. If you integrate his entire essay about "Technical Interview Rift", he essentially wants to lecture the "too cool for school" dev teams that pride themselves on Fibonacci puzzles, etc. However, he can't go into full-frontal sarcasm mode like Stephen Colbert / John Stewart because he doesn't want to make the very audience he's trying to reach tune out from his message.

Therefore, he has to dance around his intended message in such a way as to not insult his target. There's probably a better word to describe what he's trying to accomplish but I couldn't think of it so I called his passive-aggressive tone: "sarcasm".