Is it rust in my plant?

Probably just had a few beads of your neem oil on the leafs that ended up burning your girls. Spray about an hour before lights on to give them time to soak up that neem oil mix. Also your fans should have dried it after an hour. Happy growing!

Always treat plants at sun up. When it's not beaming hot and bumping. That is when ud naturally find dew and moisture on the leaves of plants and grass.

You answered ur own question there fam! 100% what it is.

Maybe it's because I watered the leaves the other day with neem and it was a burned a little bit by the sunlight

Doesnt look like rust to me.some of the The rust fungus spores and color will wipe off on paper towel or tissue. Do this to check for rust. Also when looking at rust on a leaf it will look like a 3d object on the leaf surface, not one with the surface. If u have a microscope u could use that as well to identify the rust fungus and its spores. I dont think that's what that is though.