You have it half right, in my opinion. In the first half of rule 3.7, where the balls are close but not touching, then if you shoot forward and the cue ball travels forward at the same speed, then you have double hit the cue ball and it’s a foul. So if the balls are close and not frozen, you are right.
The second part of rule 3.7 is an exception. That provides that if you shoot straight into a frozen CB, it is not a foul as long as it’s a normal stroke. This is so despite the fact that the cue ball is going to move at the same speed as the object ball. That is why it is important to have the referee declare whether the cue ball is frozen to the object ball or not.