Wow, I'm glad to hear you didn't lose it. It could have been a whole-lot worse.
I like the netting bungee cords, lots of hooks, and you can really strap them down.
Years ago, I had something similar happen. Not the same cause. I was about to hop onto I-95 south of Ft. Lauderdale FL, a foggy, cool morning, and it was maybe 400 ft to the on ramp.
Suddenly my rear wheel locked up, and I was slewing L & R and was able to get it stopped, upright. It was a 4 lane rd. Luckily no one behind me was texting (it was before that was 'a thing'). I was next to the shoulder, a short distance from a car repair shop. A mechanic came out of the shop and helped me get the bike to the side of the road, entirely off the traffic lane.
Turns out the transmission bearing behind the countershaft sprocket had its outer race split completely in two, and that locked the engine. I'm lucky it didn't end up much worse for me. I'm glad you only lost your bag, and that you escaped serious injury or worse.