Its been probably twenty years since I flew at Wycombe Air Park, but the same sort of close encounter used to happen there on a regular basis, so I wonder if that's the airfield where you experienced this not quite an airprox....
A lot of traffic used to happily power without any radio clearance of any sort over that busy hub at "2,000 feet!" thereby being in theoretical correct altitude to avoid the bottom of the Heathrow zone, and the top of WAP's airspace. To say nothing of circling gliders, returning tugs, and helicopters bouncing up and down.
I intended to go cloud flying one afternoon in a Booker glider, so for the first time, before being airtowed, set my altimeter to QNH....and then, losing situational awareness, pulled off the airtow at 2,000 feet...wondering why the ground looked closer than usual! It was, of course.
Our only defense was a keen lookout at all times, so I trust your student has learned that lesson....eyes on stalks and trust nobody!