i wouldn't flip out at the moment... you're more likely to damage them trying to treat what you THINK is an issue... than you are to preemptively fix an issue that probably isnt an issue at all.
wierd shit happens to leaves all the time. its impossible to tell if its a systemic issue or a single isolated issue without observing the problem area for a few days.
if its a fungal lesion or bacterial spot( i doubt it). let it manifest clearly... the spots should go totally necrotic and spread getting wider with a ring of semi necrotic tissue around it.
if its a powdery mildew( doubt it), you could rub it off with your hands once it sporulates... leaving visible shit on your fingers.
you might check it out under a microscope if you have one.
but wont it spread to my other plants? not really. not unless you have huge humidity issues, or you are keeping the leaves wet all the time.
your plants look vigorous and healthy. i wouldn't do anything at all without observing them for a couple of days.