There isn't a requirement to monitor 121.5 in the UK the only country I know who advise it is France.
I know who the company are who was operating there and I would have thought they were using a company frequency (This would make sense in regard to safety, Lots of helicopter close together on a mountain flying course)
This said it also makes sense if you see a military helicopter in close proximity in this type of situation to listen out on 121.5