Was this Gulfstream way below the glideslope?
There's no incident here. St Martin has a very short runway which spans a small stretch of land between 2 beaches, it's an airport where jets need to be on the numbers. It's famous among plane watchers and there are hundreds of videos of aircraft coming in low enough it seems as if you could reach up and touch the landing gear. 

So if there was a glideslope this aircraft was certainly below it, however it's not an instrument landing so glideslope had nothing to do with it.