It’s very difficult to say, but hogs aren’t known for necessarily doing what we want them to do. i.e. they are just as likely to use a completely different place to the one we might have thought was ideal.
It may or may not be a female in there. But I would leave the hog in peace and not keep looking in case it is. Whether a female gives birth in your garden or not, you still might have hoglets visiting. But fingers crossed it is a female about to give birth in your hog box.