That was a quick diagnosis! But if you're sure it's right, then I see no reason to worry that it's not. For me it took a while to get the diagnosis. I think, in part, it depends on how trustworthy they find you. And I believe my BPD diagnosis (which is wrong, I have now found out) made me untrustworthy in their eyes, so they waited until they saw me in hypomania before they decided to believe me (they could have called multiple people to check if what I said was true). He probably thought you were trustworthy and insightful, and didn't see the need to wait longer to make the diagnosis. I'm glad it went well and that you got the dx.