"claiming the rolled over amount was a non-deductible contribution."

A Roll Over is not also a contribution, though, so that is a bit oddly stated.

Was it a new contribution that year? Was it deducted on that return (a new contribution) or not deducted on that return? If "roll over" is stated, was it rolled from account to account of the same type? Were they trying to do "backdoor" and if so, do you understand how to confirm this is what they did (or thought they were doing)?