@Bible Highlighter,
Here's an English scenario for you. Suppose a major building shifts a bit. The owner of the building calls up the contractor complaining, "I'm going to sue you for laying down a bad foundation."
Contractor replies, "You're barking up the wrong tree. That's not my foundation. If you recall, you decided to hire out an independent contractor just to build that foundation. That's
the foundation of the Bartlett and Son's company"
That's a genitive of originating cause. It parallels "the foundation of the apostles and prophets". Notice that the foundation doesn't CONSIST of Mr. Bartless and his sons (that would be an absurd reading). Rather it is a foundation LAID DOWN BY THEM.
As that scholar already warned us - that's the position of the majority of modern Greek scholars.