The reason Photoshop None reports a score of 20 is that there are no sequencing rules in the "None" example. If you look at that example, there are five children of the root activity. One of them is the test.
If you pass all questions in the test, it will have a score of 1.0. The other four children have no score.
The default score rollup sequencing logic is to take a simple average. So 1.0/5 = 0.2.
The proper way to implement that course would be to have an objective measure weight of 0 on the other four activities that don't report a score.