I would firmly say that it did not act reasonably. Blocking the other lane of traffic is the second worst action I can think of, only behind ramming into the emergency vehicle. It would have been better to ignore the emergency vehicle and continue driving, which would have at least cleared the jam.
I worked in the space at one point, and I would put the issue down to autonomous vehicles being trained entirely to keep themselves safe. E.g. they know to stay a certain distance from other cars, but they have no concept of "could another get around me?". A similar example would be parking. On a street without lines to mark spaces, I would not be surprised to see an autonomous vehicle park in the middle of a space large enough for 2 cars, preventing someone from using the rest of the space. Another would be opening space for someone to merge. I don't think that's something they ever do on purpose.
We're teaching them to not hit things or get hit by things, rather than teaching them how to drive, which is a far more nuanced skill. The same thing would have happened with 2 autonomous vehicles, because neither even attempts to understand what the other is trying to do. They would just deadlock until the garbage truck moved.