Confusion over face masks at Eastbourne hospital

I had a appointment at Eastbourne DGH for a X-ray on my hips. I got to the hospital, used hand gel and I was stopped for using my own face mask which is from trusted PPE and is adjustable around the ears.

The lady who stopped my was saying when you come into the hospital you have to wear a clinical face mask, but on the appointment letter and outside on the windows of the hospital it says use a face covering it does not say use a clinical face mask. When I was waiting for my X-ray I saw three people who had there own face mask on!