someone had thought it was a dry well? any issues with foundation over it if it was a dry well? might have drainage problems?

I don't know but I wouldn't trust the excavating people to make the decision. But I don't know who exactly would have that answer. Maybe an engineer.

Or an old shallow well? Some additional info about the property and dimensions and other descriptive details regarding the hole in the photo would be helpful....was there a house there before, for example?

here's some other pictures, to help to see the size. Should it be much of an issue? Just fill it up with gravel and then can place rest of foundation on top?

Looks like an old cistern. Used to be for collecting and storing rainwater.