Offset is a power technique, designed for climbing and other high resistance situations. Two Skate is a high speed technique.
So you might think they would be hard to confuse, but beginners often struggle to see the difference, probably because both techniques involve poling with every other leg push. Or maybe it has something to do with confusion over the homemade technique used by self-taught skiers.
This video will help you develop your eye for identifying skate techniques like a pro.