Don’t worry about the hog ignoring the slug – especially if it was one of those big ones. It is the smaller or medium sized slugs that the hogs will eat. The large slugs are the ones attracted to the food put out, so sometimes it looks as if the hogs ignore slugs in general. In reality those larger slugs are a bit big for hogs little mouths to tackle.
But the hog will probably go away after it has tucked in to the food you offer and forage for beetles, etc. In general, beetles, caterpillars and earthworms are thought to form a larger part of hogs’ natural diet than slugs do. But the small slugs are so tiny that it would probably be really difficult to actually see the hogs eating them – especially as they are more likely to be found amongst vegetation.
Some hogs don’t seem to take to wet cat/dog food, but cat/kitten biscuits are fine. But make sure there is always plenty of water available if feeding dry food. It’s best in any event to leave water available all day every day, even if not offering food as well. It’s more likely hogs will be able to find some natural food then it is to find natural water sources. Wide but shallow plant saucers are ideal for water.
Good luck. I hope you continue to enjoy the hogs’ visits. Happy hog watching!