It can even happen to me, in front of my very eyes. The rest of the trip left little to be desired. It's a sad fact, but there are con-artists out there far more clever than the man you mentioned. Purses routinely disappear from between slots or from the backs of chairs. Chips disappear from tables.
Some criminals even work in teams.
After all, he did not know you were only 10 feet away, he did return your money to you without hesitation, and he was already on his way out the door. The bottom line is that you must take all measures to protect yourself and your belongings. You must be on your guard. Ultimately, it is you who are responsible for your valuables.