Old fashioned Catholics do it to the Lord before we enter or leave the pew.
Tebow’s family was busy teaching Filipinos that Catholics were pagan ignoramuses and not really christians, so although we do it all the time here, I am not sure he realized where the gesture comes from.
Why the press didn't pick up the Catholic roots of his genuflection is the real question. guess none of them are Catholic.
The source of the genuflection is from ancient Rome: soldiers would genuflect before the emperor as a sign of respect...