It is his money and he can do whatever he wants with it but I hope he refrains from doing it often. The practice carries the potential of attracting fake scandals and opportunists.
One of social media's pitfalls is it ability to communicate vast amounts of information that can be disseminated by individuals wanting to take personal advantage to get their 15 seconds of fame. Next time, a waiter may recognize Prescott and remember this story but Prescott may believe the waiter does not deserve a $1,000 tip. Or next time, another waiter may have read how Prescott tipped $1K and considered he or she provided a $2,000 level of service because their mind is warped like that. Scenarios can vary but they all could result in someone being disgruntled, taking to social media, and twisting the situation to serve their own misplaced ego.
Then again, any celebrity should comprehend the pitfalls of interacting with the general public and act accordingly. Kindness is a virtue but dispensing it without forethought can make anyone a target for malicious foolishness.