Certainly agree with Ed that your apple doesn't sound like a Mutsu,
which I grow here and is a round, slighly flattened apple. I also have
Criterion, which is a dead ringer for Red Delicious in size and shape,
but greenish in color unless it is left to hang very late, at which
point it turns yellow with a pink blush. Criterion is very crisp, but
if near ripe I would not describe it as a tart apple, no more so than
Red Delicious. I use it almost exclusively to produce dried apples, a
use for which it is admirably suited.
Miller Nurseries has carried Criterion for many years as one of their
flagship apples, and the possibility of a mixup certainly exists.