Are you really saying he should not enter the atz when the runway is under him?
No, not at all, but if "the runway is under him", it's a bit late to consider ATZ entry procedures when a pilot is already as far inside the airspace as one can get. Airfield procedures and airspace are there to prevent an incident like this from occurring. The Full Sutton frequency is published on the CAA VFR charts.
Pocklington is only four miles from Full Sutton so I would have thought the glider pilot should have thought about this local radio frequency well before this incident, especially as he was relatively well experienced.
In any event, hopefully the publication of this report will serve it's designed purpose, namely to allow others to learn from the mistakes made, which could have had far more serious consequences.