Tagesschau, citing the federal police, reports that two cables at two locations in germany were cut https://www.tagesschau.de/inland/bahn-sabotage-101.html

The locations are a few hundred kilometers apart.

That doesn't mean it wasn't a state actor, the act itself can be done by anyone but knowing which cables to cut for maximum effect does require knowledge.

Considering it was two cables I wonder if they were part of the same fibre ring. Usually with those if the cable gets cut the traffic can route the other way around the loop. This is why they use rings instead of simple links.

It's because fibre cables are easy to cut by mistake, a digging machine will cut through it without knowing. Unlike the old backbone cables of old that were thick as a sewer pipe and carried thousands of cable pairs and heavy armour.