I dug up my buddy's FB posting....
On a $28.89 bill (tax included)
18% is 7.27. Should be 5.20
20% is 8.08. Should be 5.78
22% is 8.89. Should be 6.35
Yes, I agree the manager is probably in on this, but he needs to know he's been caught. Let him know you have numerous friends who dine there and you will let them know what is going on.
I think perhaps his meal was somehow discounted and the tip calculations were based on the full amount but without seeing it, no way to be sure.