The terms are very clear. Apple wants to control distribution of apps, the enterprise program is only supposed to be for employees or for end users using under the direct personal supervision of an employee as part of an in office test. The conditions are clearly defined.
Given that the users of the app in question were being paid by Google, one could argue they are employed... or at least are contractors.
On the other hand, given the users did not have the rights generally associated with being an employee or a contractor... and they were not even getting minimum wage...
But at that point IANAL and courts would need to decide
Google or FB isn't going to touch that with a 10 foot pole, and no there is no need for courts to decide, they don't want these users considered employees or contractors in any way. Also monetary compensation is very common in some research industries without said people being contractors or employees. Simply put Google and FB F*up big time in violating the TOS.