Having been there that afternoon on Stand 10 at EDI, I know that the gentleman did NOT go through security and to the gate by himself. It was unfortunate that there was a very inexperienced (new) member of staff working for the company tasked to deal with PRM passengers at EDI that day.
It was even more unfortunate that the crew were put in the position they were and under the circumstances (as stated previously), - made the right call after clarification with EasyJet Ops.
I can also confirm that for anyone travelling "alone" with any disability there are a few things they must be able to read and confirm an understanding of fully "prior" to being boarded. - This did not happen.
The situation should never have been able to develop as it did and as ever is the case, a rolling culmination of factors contributed to the end result being what it became.
The Captain did a great job under the circumstances dealing with things. As said previously, just because this individual may have travelled previously on their own, - this tells me nothing other than the travel prior may have been allowed and undertaken wrongly.