Do you think my friend has the right to be upset and angry at me?

here is what happeneed. couple of months ago, my friend send me message on aim about how well he did in school and everything. He told me he got like a 90 on his chemistry exam and physics exam. I was offline on aim then, but i got the message. I forgot to reply him back. The follow next week after he sent me the first message on aim. He sent me a second message complaining that i never praised or complimented him and he started complaining how i am not a good friend and everything. From since, he has been ignoring me and pissed at me because I forgot to say good job. I called him today and he picked up, i know he was there, but then he hang out the phone. DO you think I clearly did something wrong here or does he wnat attention so bad that he needed my praise? I thought it was something trivial, but to him, it's something significant.