I think he's probably increasingly chimping out, like Gary Groth described him behaving in an office environment, but having destroyed more than one iPhone in a squalling, crying, screaming tantrum already, he knows they're too expensive for that.
So he's texting because he can't control himself verbally, but increasingly losing his shit as he continues not getting what he wanted, which was apparently to bully some dude into denying that he was bullied. He has no idea what a complete piece of shit he looks like in the cold light of day.
He sounds like a crazy stalker ex, and he's some guy who's talked to this dude maybe once or twice. What a mental case.