Hi @sticksandbugs, From what I've read, PMR often occurs after there's an injury, illness or something that causes the immune system to go into overdrive. I was doing a lot of walking and walking backwards, hurt my ankle, and a few days later, I had extreme pain from the neck down throughout my body. My maternal aunt got it after she hurt her knee moving furniture, and my mother in law got it after she returned from a long trip. All three of us developed GCA. Onset following an injury was pretty quick for us.
You were in pain with your hamstring a long time. My hunch is that it probably didn't trigger your PMR, but your hamstring probably was inflamed, which is why the prednisone helped.
Take care.