Hi cececat
A few possibilities.
Hogs will sometimes make more than one hibernating nest, so may not have hibernated in that one at all. Hogs are also known to change nests during hibernation. But it’s possible it could also have decided to come out of hibernation early if there is food around.
The way you describe it, “almost like they brought food inside, ate some and then spat it out”, sounds as if a rat may have been using the nest. A rat used an old nest here once and it looked a bit like that. I wouldn’t expect hogs to take food into a hibernating nest, although some hogs sometimes build nests in their feeding boxes.
A completely natural hibernaculum would be outside anyway with maybe only hedge for cover, but if it is well built (and especially if made with leaves which can be overlapped like tiles) it should be pretty waterproof. Medium sized leaves seem to be hogs’ natural choice of nesting material, although some long grasses are also useful to weave the structure together.
If the space within the brick structure is quite small that could be a limiting factor as to how waterproof a hog could have made the natural part of its nest. The drawback with plastic is that it can cause condensation and make the nest damp that way, so I tend to avoid it.
There probably isn’t much ‘wild’ food around at the moment, so sounds like a good idea to offer them food (and water) if they are out and about again.
Happy hog watching!
