As others have mentioned, it's a Bustamante thing, whose approach and technique then has been proliferated amongst Filipinos. It's not just that he goes behind his back. He goes behind his back on a wide range of shots with every imaginable cuts and position play. When the vast majority of players were going behind their back, the shot almost always is relatively straight forward with minimal cue ball demands.
Every player has obviously done the behind the back thing, and the first pro player I saw on TV do it was Mary Kenniston in the Brunswick World 9-ball Championship (which she won). But, it was a relatively simple shot, as would be expected.
It was really Bustamante more than anyone else that sort of showed that certain shots, going behind the back isn't just a bar room show off maneuver, but actually is the right shot in certain situations, and that those shots aren't limited to simple ones. You'll see Alex (who can shoot left handed pretty well, and can use the bridge very well) will also go behind the back on certain shots.
Freddie <~~~ pinoy with no behind the back skills