It's not that strange that someone would park on a sidewalk. People do it when they are moving furniture or building supplies. Sometimes people do it if they just need a temporary place to get off the road. That guy might have done it so the truck didn't get buried by the plows. I'd blame the accident more on the weather than where the guy was parked.

And sometimes you have to ride on the sidewalk for a bit - nothing wrong with it, just be careful. But yes, if no one saw, pedal like hell.