'I had no idea blood vessels had that much "slack".'

I'm going to take a guess at this.

Train wheels are around 3" wide and flat, with a 'cutting edge' rim on the inside of the wheel. The rim keeps the wheels on the rails, the flat part carries the weight.

If a human body falls outside the train with legs underneath, that cutting edge is what literally cuts off the legs, but that wide flat part is, at the same time, crushing the flesh and bone above the cut. That's why you never hear of train amputations being reattached -- too much damage.

In this case, the crushing effect probably turned the lower part of what was left into hamburger/jelly, and the arteries may have pressed closed. Arteries and large veins are fairly heavy-walled, so he may have been able to grab the uppermost part, pinch it off to stop the flow of blood (if the crushing action hadn't done most of it), and tie the knot.

He might have had 3" of artery to work with, but it still took an awful lot of manual dexterity... and with shaking hands, probably.

He was good, she was lucky.

Sue