It's not even close to an NCAA violation. The OP has no ties to either the athlete nor his institution - the OP is neither a duke alum nor a booster nor connected to either. By buying the dinner, no competitive advantage was gained for Duke or an opposing school by either lining the athelet's pockets or trying to lure him away.
Once again, the uber-knowing let's run crowd cries wolf and makes a mountain out of a mole hill.