What you've deleted here is a public right of way, part of Ivinghoe Footpath 27.

If the PRoW tags were applied to the wrong path, it would help if they were applied to the right path. This may help, although I'm sure NT has access to better information about PRoWs which cross its land:
https://osm.mathmos.net/prow/progress/bucks/-/ivinghoe/

If you have a desire line path which is visible on aerial imagery on National Trust land where you are, as the landowner, in a position to forbid access, you'd be better off using:
highway=path
access=no
informal=yes

https://wiki.openstreetmap.org/wiki/Why_can%27t_I_delete_this_trail%3F