It sounds to me like he was just trying to make a transition from the e-mail topic and was agreeing with you (the "Okay" first) and was just moving on, not wanting to argue or get picky or. . . whatever :-) But his abrupt shift was not a good choice since you were still mired/interested in what you were talking about and not ready to shift. I would try not to take it personally. I think it was about the topic, not about you or what was being said. He just had something else on his mind and wasn't paying attention. He definately goofed!

T's don't generally play "games" trying to elicit responses from you unless they stay with it and make sure whatever they're trying to do gets done. So if you're confused and lost, it's probably not deliberate on his part, just some little thing that happened that he didn't pick up on it's ramifications with you. In a "normal" conversation, if a friend had said that to another friend, the other would have said, "What do you mean, 'Whatever'?" with a bit of humor or annoyance/anger in their voice and gotten it cleared up. I don't think it was meant to hurt your feelings.