On the CCR side it doesn't say anything, but on the GF Lounge side there is signage at the top of the stairs saying "For Emergency Use only", which would seem to apply to the gate to the area behind the kitchens too.

I suspect the gates are unlocked as they are on an emergency escape route. However, I cannot believe that anyone would view nipping round the back of the kitchens as a legitimate route between lounges.

Sounds to me like a case of self-upgrading.