I agree, that doesn't constitute reserved airspace - looks like it was still in class G. Bad airmanship not to recognise and avoid it though.
I am an avid user of GPS, but not for flying. Surely it is possible to programme any location as a waypoint using either Lat/Long or OS grid refs? Or would that be too time-consuming?
These days I use GPS (moving map) every time I fly, VFR or not. It's absolutely routine to programme user waypoints as lat/longs, such as a turning point or a landing site in a back garden, paddock or at a hotel, for example. I always re-check the co-ordinates then review the route to confirm it matches the lines on my chart.
The problem we appear to face is that folk either don't actually know the fundamentals of detailed flight planning, or fail to implement them correctly once
en route.