In general it’s not a good idea to disturb them in their homes, but you said that was yesterday, so possibly not the cause. It isn’t normal for them to be out during the daytime. It might have come out because it was really hungry, or thirsty, so you did the right thing offering food. But don’t forget to offer water all day every day – very important. They are probably more likely to be able to find some food in the wild than water. But I would also continue leaving food out.
Often being out during the day is a sign that something is amiss, but at the moment it might be difficult to find a hog carer/rehabilitator because of this virus. But if you see the hog out again, and especially if it looks as if it’s sunbathing or behaving oddly, it would be a good idea to ring the BHPS on 01584 890801 to find your nearest carer/rehabilitators and take their advice. You will be able to explain exactly what the behaviour was to them. Hopefully it will be o.k. having had a good feed.