I think I can answer this as I’m the gentleman you’re referring to. I believe your assessment is correct, I was leaning far over my bars and in fact pulling myself forward with each rotation of the pedals by pulling on the brake hoods for leverage. I had so much forward force in motion that I essentially catapulted myself over the bars and (I think?) I maintained my grip on the bars throughout the somersault thus pulling the bike on top of me once I hit the pavement.
But here’s where I’m still not sure what happened....... my chain is not broken!!!
I was in the garage moments ago as I’ve been laid out on pain meds unable to move a great deal so didn’t see the bike until now. I will eventually take it to my LBS for repair and I suppose only then will I know what the heck happened. All I can describe is that it was like throwing a transmission into neutral while going full speed.