Pixilate, as well as turning normal type moves into fairy type moves, also boosts the move's power by 1.3 times. Moonblast has a base power of 95, which is normally higher than Hyper Voice's base power of 90. However, after the Pixilate boost in damage, Hyper Voice's base power becomes 90*1.3=117, a whole 27 higher than Moonblast.
The move doesn't become both normal and fairy type like Flying Press becomes Flying/fighting. Hyper Voice is counted as simply pure fairy type when the Pokemon using it has Pixilate.