It's just a glider site with 3,000' launches. Like a lot of glider sites (mine included) they fly Wednesdays as well, it's known as old duffers day. Saltby often have a semi permanent Notam on, 'intensive gliding' etc, not a competition or anything, just them doing what they do every day. I have a feeling that the nice lady on ATC was getting mixed up between Notamed and just being 'active.'
Maybe they were just being over cautious. Nothing wrong with that.