It looks like insect damage. I had some tiny little callused over chew marks and some yellowish specs. Turns out, I think they were moth eggs and when they hatch, they are a catipillar that does a lot of damage if left unchecked. You have to check all the time until you kill every last one of them.
There's a possibility, they came from bird shit that dropped on the leaves.
If it's insects,
check the stem parts of your leaves connected to the stem. You'll find bruising from the bites and a trail of bug poop.
Follow that trail to the tops.