An engine with no oil is not going to make it more than a mile or two and any symptoms (oil light, knocking, etc) would be readily apparent.
There is no way on earth this person drove the car home, parked it for a few months, took a 300 mile trip, and THEN discovered there was no oil.
If you had left the oil out the car owner would not have made it home much less a 300 mile trip in it.
Bottom line is that this car did not move that far with no oil in it - period. If one used the argument that you did indeed leave the oil out then why did the car owner ignore the oil light? Why did they ignore clattering valve lifters, which are going to be rattling? Why did they wait several months, take a trip, and NOW complain?
Something has occurred with this car and they’re just looking to pin it on somebody. Engine burning oil like a bandit, car loaned out to someone with a lead foot, possibly hammered the car hard themselves, who knows?
My feeling is that it’s an oil burner or may have overheated badly in which case it then became an oil burner.
Inspection of the spark plugs and tailpipe could help determine this.