I am pleased to read your post because I have had a similar experience. I put a new Hog House out a couple of weeks ago, along with Hog-Cam (the best birthday present ever!), and was delighted to see a Hog moving in immediately (within hours!).
We called our Hog Rudi; then last week Hog-Cam revealed that Rudi has a friend! The first footage did not show whether they were sharing the Hog House, but did show them sharing their food very politely and getting on fine together. Then at the weekend it became apparent that they are sharing the Hog House! I was very surprised because I too read that they are solitary animals, but Rudi and Judy (we assumed the second was female because it is smaller, but from Nic’s post it could just be a young Hog) seem to be best friends.
I was also wondering whether to continue leaving food out – I think I will; as Nic said they may move once or twice during hibernation. For the time being, the Hogs still seem quite active and are certainly coming out for their dinner and a wander every night 🙂