Why would someone fill a hole like this?

Digging up a patio at the bottom of my garden and came across this filled hole under 2 layers of paving. Is this just a terrible way to fill a hole or is there a purpose to this?

For context : the plan is to excavate this and fill properly due to it being where I want to build a new foundation for a new shed.

While I can’t see the bottom for sure it seems to be pretty deep.