Every University, business and organization that receives grants has overhead rates. These vary from reasonable to ridiculous based on the organization.
These overhead funds then typically go into a larger, not grant specific, fund that is fungible. The spending out of that fund is then restricted not by grant guidelines, but by the general rules of the institution. Usually that is still somewhat restricted at a University, for example, that usually won't allow alcohol. However, businesses receiving grants generally have fewer restrictions.
If you want to look at how overhead is used out of those general funds, I'm certain you will find this at any recipient organization. I am in fact surprised this is all they found. The fact that they are only looking at NSF and focusing on politically controversial topics for their specific party is very suspect. Should we start looking at how defense contractors spend all of their overhead for DARPA awards? Would they even share that information like NEON did?