Take a small sample and place it under a microscope. Fungi have distinctive features when viewed under the scope.
Usually need a stain to view fungus properly, such as lactophenol blue. And if it were a mold-form fungus it is best viewed under a negative pressure hood to minimize risk of inhalation. fwiw
I think it is crystal formation. The watch is trying to morph into a quartz... 😁
Or buy yourself an electron microscope so you can really zoom in on those suckers! $100k of equipment to analyze a $400 watch...yup, sounds like Omega Forum to me!
You’re much meaner than I imagined 😲