It looks like it's probably damage from thrips. They can infect a variety of plants, and do damage that looks like that.

Spider mites can do similar damage, but the specks on the leaves are often so small and close together as to make the leaves look stonewashed (and spider mites leave webs).

Some say some chemical pesticides can actually increase future thrip infestations.

One of the more promising things I've read about in controlling thrips is beneficial insects (like lacewings, spiders, etc.): see https://homeguides.sfgate.com/citrus-...

I can't say if this is citrus thrips or another species, if I'm right.