I would do as advised by the hog carer. The hog sounds quite light and I expect you’re right, probably came out during the day because it was very hungry/thirsty – so would probably benefit from a bit of feeding up before releasing again. As I understand it, it’s normally recommended for a hog who has been in captivity to be 600g before releasing, because they tend to lose a bit of weight on release. Hopefully it will put on weight quite quickly.
If it’s otherwise healthy, I wouldn’t keep it in too warm a room, so that it won’t find it too much of a shock to the system when it comes to release time. But provide a nice ‘nest’ of either a small towel it can burrow under or paper torn up in strips. Leave it a constant supply of water. They’re very good at spilling it, so you might need to check from time to time during the day.
If Stef’s around, she may be able to add something to this.