Whether his assessment is accurate or not, the reasons you question it are totally valid!
Very little time spent, a few questions, and bada-bing a dx?! If your hypo
was in fact the caused by the sertaline.... the DSM
specifically disqualifies this (substance-induced) as a criteria to base dx upon. It is also legitimate to wonder about the accuracy of self-reporting. Just ask a statistician, lol.
A "few very short questions" is troubling, isn't it? Please excuse, but it compels me to rant

...

Rant the first...That is the very thing that caused my initial mis-dx. As MDD. She undoubtedly felt she'd 'seen it enough' to consider it easy to dx. And, to ascertain the manic end of things? 3 words(!!!) "So, no highs?" I thought she was talking about drugs. I was in no state to self-report, or
even realize I needed clarification/elaboration(!) Hell, I couldn't rub 2 brain cells together. If she'd asked someone else? The answer would have been a resounding, "
OH yeah." Followed by voluminous elaboration, lol. My hypos are
not subtle. Even slightly more responsibility in dx-ing would have easily uncovered that and saved a lot of hell.

Rant the second... Especially now, on account of computers, it would be all too easy for someone to memorize a list of symptoms that might well "pass" a cursory questioning. (This would anger me beyond the power of 10,000 suns, but surely it happens.) Not to mention people's tendency to self-diagnose and pathologize the ordinary. More in-depth interviewing would weed out a lot of that kind of crap.
A few short questions simply don't suffice in such serious matters! To your perturbation by it, hear hear!