Re: upset with the professor
well i can't say why he wasn't giving you the credit to begin with but when he told you that he would 'give it to you if it would make you go away', he was giving in and was prepared to give it to you.
it probably annoyed the hell out of him when you just went away - after all the explaining, if you really thought you deserved the credit, when it was offered to you (in whatever circumstances) you just walked away, so he probably feels you wasted his time for nothing.