My question involves a traffic ticket from the state of: Massachusetts

I was traveling on the right lane of one-way two-lane street when I noticed a car stopped ahead of me. I pulled up behind the car and stopped. Then they put their blinkers on and started parallel parking, neglecting the fact that I was behind them. There was traffic in the left lane, and there were other cars behind me, so I had no place to go and avoid the car that was backing up into mine. I honked so they would stop, but they continued moving in reverse to parallel park (this is all while my vehicle is completely stopped). The driver side of their rear bumper collided into the passenger side of my front bumper. After the accident, the other driver is claiming that I was trying to pass them (on the left) at the time of the collision, which is false. They have admitted to moving in the reverse direction at the time of the collision.

Given that my vehicle was stopped, and their vehicle was moving in the reverse direction to parallel park, aren't they 100% at fault?

Talking to my insurance, the adjuster mentioned that in some cases the car that is parallel parking has the right of way. At the same time, I have been told by others that moving in reverse on a one way road (even when parallel parking) puts one at fault. Any comments on what the law says? I haven't been able to find any information about the rules governing right of way while parallel parking in Massachusetts.