I went to a reasonably posh private school, but Scotch is next-level. (As I think I've noted here previously, it's rumoured that the annual budget of their rowing program is higher than the annual budget of Rowing Australia).
I assume they've got that much land because they've always had that much land, which is the way it sometimes works. Winchester (where I worked during a 1989 gap year) owned a couple of square kilometres of land in a pretty densely populated area of the UK - apparently the story was that if they sold it it would trigger a tax bill which would send them broke.
Still, in terms of odd things that private schools own, I believe that Prince Alfred College in Adelaide owns several percent of Coopers Brewery (the shares being left to the school by one of the original Cooper family).
They should send all the students back to (physical) school -except the boarders. With so much space, social distancing can't be a problem.
It really is next-level Blair! And yeah given where it is I can't even begin to imagine what the land would be worth!
Haha - well, I hope Prince Alfred give their school leavers a good exit package in that case? Seems only fair.