No, your Yamask doesn't have perfect IVs.
If your Pokemon's average IV is 7.5 or below, the IV judge will say that its potential is decent.
If your Pokemon's average IV is 17.5 to 22.5, the IV judge will say that its potential is above average.
If your Pokemon's average IV is 22.5 to 28, the IV judge will say that its potential is relatively superior.
If your Pokemon's average IV is 28 or above, the IV judge will say that its potential is outstanding.
The IV judge will then proceed to tell you the Pokemon's best stat.
If your Pokemon's best stat is from 0 to 15, the IV judge will say that it's rather decent.
If your Pokemon's best stat is from 16 to 25, the IV judge will say that it's good.
If your Pokemon's best stat is from 26 to 30, the IV judge will say that it's fantastic.
If your Pokemon's best stat is 31, the IV judge will say that it can't be beat.
If a stat is perfect, the XY IV judge will say: "Incidentally, I would say its greatest potential lies in {insert stat here}, stats like those... they just can't be beat!".
If there's more than 1 perfect stat, he'll say: "Incidentally, I would say its greatest potential lies in {insert stat here}. But its {insert other stat here} stat is good, too." etc.
Bulbapedia - stat's judge
