These AVs are programmed to give high priority to police cars, ambulances, read works, and what not. They're also happy to interprete what they see in the strictest way possible.

IIRC, there was a YouTube video of one of them going crazy because of a traffic cone... then running away from the operator when they tried to override and correct what it was doing.

It could be as little as cops leaving the car "somewhat" blocking the normal flow of traffic, then the Cruise cars strictly obeying "pull over and wait", while someone with more common sense might've reversed, gone onto the curb, or whatever.

Then again:

Cruise spokesperson Tiffany Testo countered that one of the cars cleared the scene and that traffic to the right of it remained unblocked. “The ambulance behind the AV had a clear path to pass the AV as other vehicles, including another ambulance, proceeded to do,”

...it could've been the "blocked" ambulance's drivers who were on autopilot?

Seems like not enough data to draw a conclusion.