There's no reason not to file a report. I was "kissed" by a transport truck on the 401 years ago and went to report it. I never called my insurance company, but a few days later they called me. They asked it I was filing a claim and I said to them in absolute plain English that I would not be filing a claim and I reported it to hopefully do something to the stupid truck that hit me. He only pushed in my mirror on my chevette, so it wasn't a huge deal, except for the idiot not being able to drive properly.
Same thing happened to me years ago in my car... Reported the collision at the collision centre but didn't want to go through insurance. Next thing I know insurance calls me up and asks if I want to file a claim, saying that it would impact my premiums the same regardless (since they deemed it 50/50).
Also, wasn't there a post from someone that had their bike reversed into just like this and it ended up being covered under his collision coverage, meaning deductible and future rate increase??