Not sure of the rules anymore, (seem 20 years ago since I was last there) but some routes/airspace need crew & a/c certification. That airspace block used to start above FL290. Thus is the a/c or crew was not certified to enter the vertical block of airspace it had to fly under or over. Or did you say that it subsequently climbed to FL320? That could be a weight issue or it was no longer restricted by airspace. I'm not familiar with the route.