It is definitely a weird way to commit suicide. It defies rationality, but suicide isn't a particularly rational thing to do using any method.
I don't know whether this is rational or not. But from a "what happened" perspective, the police seem sure that he blew himself up (rather than having someone else blow him up) so he is, in fact, a suicide bomber.
I wouldn't even call him a homicide bomber since he didn't kill anybody else. He may have had plans to kill others (we have no facts to show that at this time) but he didn't.
They haven't announced any suicide note, and I haven't seen any confirmation of his being "depressed" or otherwise sad and suicidal. It certainly could be suicide, or it could have been a failed homicide bombing. I hope that when we know, the media will bother to tell us.