makes me pretty upset, but I don't know what I can do. If it is some
damage caused by them, how would I go about finding out? They'll just
deny anything saying they didn't touch anything.

They could have changed the drainage significantly without doing anything
improper. It is unlikely they broke a pipe without noticing.

The sump was working when power was restored. I asked surrounding
neighbors and no one got water except lucky us.

My sumppump has not pumped in 23 years (in fact, I just found out it doesn't
even work, but have not decided whether to replace it), while other houses
on the street have water problems. In my old house I got 5' of water in my
basement during a major power outage, while the house across the street got
none. It can vary...

How much water did you get? An inch, a foot? How long was the power out?
Did the pump handle the water when you got power back? It is hard to give
you any meaningful advice without knowing what happened.