Someone tried to cut my u-lock

These cuts go all the way around this part of the lock. First, is it possible this isn’t attempted theft?

If it’s attempted theft… should I be concerned that the thieves might come back with a better tool? I leave my bike outside under a cover because I have a back injury and it’s hard for me to carry it into my apartment building. (But I could ask someone to do that for me…)

I’m not sure where this happened because it’s possible I didn’t notice right away. But I assume it happened at night, which means it would have been where I keep it locked up outside the building.

Any tips on preventing theft? Thanks!