Before the pause, "Silver" always used to mean the cadet had been on a Gliding Scholarship and had gone solo - they got Silver Wings to wear on their jumper. If they did the course but didn't go solo, they got Blue Wings instead. This was certainly the case for the last 10 years (my time in the ACO), and presumably longer.
So calling it a Silver Gliding Scholarship fits in with how it used to be. This seems more familiar to me as a CFAV and non-gliding specialist than any reference to the BGA.
There is little consistency even between different cadet forces on most things they do, let alone between cadet forces and civilian organisations, so probably not that surprising that they come up with their own standards and awards!