But it doesn't follow at all that Apple is threatening to sue them. A long time ago, in an unrelated case, I got a letter like this because I was in the room when a certain decision was made and happened to have some notes about that meeting. But there was no chance I would be sued. I wasn't the decider, and was basically a third-party involved.
This isn't law and order and that's not how civil litigation works.
Might have to make some phone calls to my local representatives now...