Or the guy flying with his nose glued to the chart desperately trying to match ground features to the chart due to winds aloft being different to those forecasted several hours ago
I know the area quite well having been at Perth for a few years. I find it hard to believe that anyone, even if they did not know the area, could have been lost since the field in question is on the north bank of the Tay estuary with a major town just a few miles to the east of it, it is also quite obviously a disused airfield.
Assuming they knew that they were on the east coast of Scotland and that they didn't think that they were over the Fourth estuary I can't really imagine were else they would have thought they would be. Much more likely I think is that the pilot either did not see the DZ on the chart/GPS, did know it was there but failed to visually identify it and assumed that his track would take him clear or did identify it but assumed that it was inactive.
As for not talking to ATC, yes it is a PPL disease but there is the possibility that s/he didn't have a radio...