C.O. Some people are crazy, flying over a glider site at 1000ft is definitely dumb if you don't call out to say hello. They were probably on the approach to Fife which Portmoak is about 9 miles straight in for so I can see why people would join from there but nonetheless not bright.
As for where you were I know the area very well indeed and would say that it required excellent lookout and a sensible approach to airmanship but isn't such a silly place to spin as you would think, lots of good fields and a runway should you need to land after an engine failure (if you're that unlucky). That's probably why the gliders spin there too. Nothing wrong with either but we are all entitled to our opinion.
As for West Lomond, Bishop's Hill - they are hardly a long way from each other!
and I've seen soaring on both, from my house and from the top.
Totally O.T. though
Just because something is legal doesn't mean it's not a stupid thing to do. It's not like there's nowhere else to fly there - bags of space to avoid the dropzone.