That wreck is 1 in a billion. There are no obvious skid marks showing that the bike slid into the ambulance (and no marks on the rear doors where a rider might strike it going over the handle bars). However, there are no skid marks from the front wheel either (from being pushed backwards by the ambulance). There is just a small white scratch on the road, most likely from the header pipes, when the bike got squished down.
In my best Inspector Gadget form of deductive reasoning, this is my best guess.
The ambulance went past is designated house. Stopped and started to back up. The motorcycle was following said ambulance and suddenly realized that he was backing up. Unable to swerve, he tries to brake but to no avail, they meet at that exact point when the motorcycle lost most of its momentum and the ambulance was slowing its backup speed down (maybe the biker reved the engine to alert the ambulance he was there or the ambulance was going 1 or 2 houses backwards and was slowing down anyhow)...TADA!!!:epimp
Either way, cool wreck (was a nice looking bike though).