I'm not sure what hard evidence you might like. There are a small number of methods by which submarine cables become damaged - anchors are right up there. In this particular case, there aren't a lot of other possibilities.
There are only two cable repair ships. It will be a while before there can be forensic examination.
Dan
This organization alone has at least 3 cable repair ships in its fleet:
The estimate for just the North Atlantic region is over a dozen cable repair ships, with the global count hovering around 60.
I think you might need to update your numbers. ^_^;
Matt