Agreed. The 'same level or lower' obviously refers to the level of the power you swap out.
So if you swap out a power you learned at level 6, you replace it with a power from the other class of level 6 or lower. You cannot drop a level 6 power to gain one of level 7 or higher.
So if you swap out a power you learned at level 6, you replace it with a power from the other class of level 6 or lower. You cannot drop a level 6 power to gain one of level 7 or higher.