James, this is a great observation.
There is a difference between Foundation and Endurance runs from the author perspective. Foundation runs are to be performed nice and easy, RPE of 3 on a scale of 1-10 which would be the low end of Zone 2, even high Zone 1 is acceptable. Endurance runs can be any point within Zone 2.
But, this is a really fine distinction. If you ran both in the middle of Zone 2, that’s a success for either type. The fine print is to distinguish them.