Interesting. First thoughts are that (1) the bullet, whilst suitable for deer, was perhaps too solid for fox and went right through with minimal expansion, (2) that it hit the tip rather than the top of the heart and so had a less immediate effect on heart function and on the central nervous system, and (3) that the fox was alert and ready to run.
I don't know what calibre was used, but last year a friend of mine shot a fox with a 6.5 x 55 at 40m from a high seat that ran around 60m despite having a significantly larger hole in its chest than is apparent in the fox in the video.
Basically, I think varmint bullets kill more foxes on the spot than deer bullets.