So sorry to hear about the poor hog. It must have been very distressing for you to find it. Sadly, hibernation is a dangerous time for hogs even in the years when the weather is better and some will always die, for various reasons. As you suggest, the younger ones are probably at most risk.
I’m assuming that the Gardmans and Dr. Johson pellets are hedgehog foods? I’m not familiar with those brands. Railways can make ideal habitat for the hogs, especially if they have wide edges which are left wild and it’s good that they have lots of gardens to visit.
I hope you have lots of hog visitors and better luck with your hog boxes this year.