Sounds like a well organized and led ride! That's pretty sweet. That sucks about mansplainin' roadie dude.
That said, I think there's a lot of defense for mansplainin' dude in this thread. The point isn't that he's the devil incarnate, but he was for sure pulling out the most common, banal, low intensity sexist crap that women swim in at nearly all times. I want to encourage you to tell him off or try to have a conversation about his behavior, but that's a lot of work to ask women to do to fix men's problems, particularly considering too many men are insecure and violent bags of crap. It might be a good idea to tell one of the reasonable dudes about how this guy came off to you--honestly, I think men like this sometimes unfortunately hear feedback about their behavior better from other men.
Hope you have a lot more fun riding. Also don't get turned off on road riding if you're interested in it, my experience has been that organized road riders often do a very good job at both gender inclusion and accommodating varying experience and fitness levels. Average social awareness and skills seems pretty similar between the two groups in my experience--that's to say, they vary.