I guess you didn't spray with something and stick em wet back under the lights eh? Probably no reason to spray if you didn't know you had any bug problems... either way, I have seen this type of spotting due to spraying with dr.doom and putting them back under lights too soon afterwards- the spots were a bit larger in places but yellow and some white even. I also used the wrong tyoe if dr.doom, the stuff I used had not only pyrethrin but also a harsher pesticide which left a rather oily residue on the leaves. My mistake and will not make it again.
my best guess would also be bugs, probably just mites though? sometimes ther are very hard to pick out till they start getting fatter. good luck, j