But not over a cable.

Submarine cables are clearly marked on nautical charts, and even recreational boaters know not to anchor in those areas.

A professional trawler captain is not going to accidentally trawl over such an area.

There's a big difference in seriousness between being able to show whether they were likely doing something they shouldn't be doing for the sake of making more money on the fishing, vs. if they were doing what they were doing with the intent of causing damage, though. But of course, that difficulty is also exactly why it'd also be a great way for an adversary to damage your cables.

means motive opportunity -- 3 for 3

given the use cases re: satellites on the island, and the continuing cold-yet-increasing tensions with Russia, it's absolutely reasonable to make that assumption

maybe they'll try to blame this on Ukraine like they tried with the undersea pipelines that got blown up, too

It's reasonable to assume. But it's wildly insufficient for either a prosecution or diplomatic consequences, especially given that all 3 also would apply to a trawler just intent on profiting from trawling.

I agree the odds are reasonably high Russia arranged this on purpose. And that's fine for the purposes of a discussion that doesn't have consequences, but not for much more.

Fishers are infamous for flaunting the rules though. I think we can only judge this if we see records of other ships in the area.

You can, at least at that specific time that all other boats were not trawling over cables.