The only surprise here is that it wasn’t from a drunk/drugged driving accident.
I would not jump to the conclusion that alcohol and drugs were not involved. Hey, I suppose anybody could get tangled up in a chain they were hauling aboard and fall overboard, but chemical assistance is not uncommon in such situations.
How does an anchor slice off a finger? I can understand bad things happening when one if tangled in a line, but I am having difficulty imaging an anchor as a cutting instrument.