In my opinion of course...you will find that the stock metallic brake pads will coat all your wheels and exhaust in a fine dust. Once moisture also finds its way there (high humidity, usually in a garage), it will only be a matter of time before it pits. That is also called rust!
The only prevention for this is to stop it before it starts. If your bike is new and you're certain you have no pitting, be sure and wipe it off after every use. Never let it sit in the garage for long perids of time without wiping off all the chrome.
Think back to a day before winter that you may have road your bike for a short period of time then put it in the garage and forgat about it for a month or so...That would be a good time for rusting to occur.
I have had this on several cars as well...My last was my F150, it's White and has little rust specs all over it, the dealer said it was rail dust. However, I did some checking and my truck was never on a train. Not to mention it didn't have it when I bought it.
I went to Ceramic brake pads, it all but eliminates the metal dust, big improvement.
IF you had no pitting when you bought your bike, then I would think it's the pads and rust.
IMHO of course!