I can't say it isn't possible, but slug damage has a very typical look- large, round to oval holes in the middles of leaves:
If it progresses unchecked, eventually the leaves will be skeletonized:
And since the slugs/snails are mainly out late at night, it is not uncommon for any slime trails to have dried up and be invisible by the time we see the holes. If you want to check my theory, come out around midnight with a flashlight and look!
What insect damage looks like depends on the insect. Earwig damage, if you have an infestation of them, can look kind of similar, but there will also be leaves that are chewed on the edges or eaten in half. You have to look closely at this picture to see that:
Japanese beetles (and other kinds) can also make large holes, but they will be even larger and at least some of the holes will be other shapes, elongated etc.
Four lined plant bugs make dark circles clustered near the base of the stem:
aphids and other sucking insects don't make holes, they just leave scars that discolor. Eventually the leaf starts curling/ crinkling:
Sorry, but I think it is fascinating that you can frequently identify what your pest is by the damage it leaves, without ever seeing the pest. I've done some study of it.