I'm afraid you're going to be disappointed!
I was initially struck by how long the toes/claws appeared, and my first wild guess was also Raccoon. At that point I had no idea whether Raccoon was known to occur in the area. However, the area is known as a nature reserve, so it is presumably reasonably well covered by naturalists who enter records into the
Observations.be database. A few clicks later, and I came up with a list of mammals recorded in the area over the last twelve years. That's
here. It's quite a modest list, which doesn't include Raccoon, or, more surprisingly, Fox or Badger. Given that the prints consistently show four toes, that also tends to rule-out Raccoon or any mustelids. As Fox has apparently not been recorded at the site, I'm left with the reluctant conclusion that the animal must have been a dog! I can only assume that the hard ground meant that only the claws made an impression, so the apparent pad shape is completely misleading. I'm still open to alternative suggestions, but for the time being I'm stuck with the idea that it was a dog all along!