It does appear to be velvet. The larger spots are normal stress marks for a naso.
Upon zooming in the white dusty look is what leads me to believe it's velvet.
This fish needs therapuetic copper ASAP.
If you can't get meds until tomorrow then the best thing to do is a FW dip for 5 minutes to provide temporary relief.
Tomorrow I would start copper and do a 90 min acriflavine bath.
All of the fish that shared a tank with this fish need treated with copper and your display will need to be fallow for 6 weeks to erradicate velvet.