It’s called “bottom trawling” and it’s pretty much what it sounds like.
Also known as cruising?
It's at least possible - drag nets can and do touch the bottom.
As do crab pots and lobster traps.
Pots and traps tend not to get dragged. Nets do.
It's conceivable for a crabber / lobsterman to damage undersea cables. It's far more likely that it's a net fisher.
Russia has a pretty remarkable set of nuclear submarines designed for covert ops. You don't see anything on the surface when they mess with cables.
Why in the world would they cut the cables to friendly Vietnam, or for that matter Svalbard, which has a Russian town of Barentsburg?
Does Svalbard really have a huge e-commerce sector or something that needs undersea fibre? They doubtlessly have plenty of satellite internet, so this will just limit their bandwidth and maybe interrupt things temporarily. What's the strategic value in cutting it?