Well, he wasn't wearing the mask anyways and he still had it when that scene showed. Maybe it was a demonstration that he could hold back Veldora's aura or something without the need of the mask.
Not sure if it was aura suppressing, or magicule suppressing (or if they're different things as it is). I don't imagine it's magicule suppressing, since that would handicap him in a fight, but maybe prevents leakage.