People who mean "Well, actually ... [with "you ignorant doofus", or worse, implied]" greatly outnumber "Yes, and" or "Totally with you on this" ones (who skew #ActuallyAutistic) ...
... especially among men talking to women.
Hence, 'splainy reply guys.
I might also add:
there are #ActuallyAutistic people out there who, because of unresolved misogyny, bad socialization, or what have you, sometimes adopt the "'splainy reply guy" script because in some circumstances, it sort of works to get what they want -- because our overall society (thinking USA here, but it's true many other places) is pretty hostile towards women and especially women demonstrating expertise.
Crossing that bridge is hard. You can't do it as it's happening, because that just sounds like trying to 'splain the 'splaining. And people who assume a splainy guy by default aren't exactly wrong, either. Most of the time, it is a splainy reply guy and #ActuallyAutistic people are on the wrong side of the stats.