That doesn't look natural, and it definitely doesn't look like an accidental rip or accidental damage. Looks exactly like something eating at the leaves. Cats are possible, but I'd think the marks would be bigger than that. My first guess is a rouge grasshopper. Not sure if you see them around often but that's my first thought.
Fungus gnats don't eat leaves, and the insects that do, don't stop eating until the leaf is gone. You'd also be able to see the insects on the bottom of the leaves. Keep an eye out for a rougue cricket!