Think of it this way: what if the author had titled it "Escaping Ubuntu containers" ?
Let's make it realistic and say he had used RedHat OpenShift as his target and example for the exploit. I'd be completely fine with the title referencing that exact product by name.
Why would he have to dance around what he is using in his demo? Maybe that concrete product has multiple layers of security or lacks them, or uses a certain version etc. He can only speak to what he himself was using and testing. "Escaping Docker container..." is the best short description (as you would need it for a title) of this demo exploit I can think of.
How would you reasonably talk about "Linux containers" without having a very exhaustive list of all existing implementations and testing all of them? If one of them is not affected you are now factually wrong.