Am I missing something or is the only thing that makes this different than so many other "insider" claims is that this guy has a career history that implies he isn't just another crackpot spewing theories? It reads just like so many claims like we have heard in the past, but this time people think the guy is more reliable. It is pretty funny that the one of the people often quoted who backs up Grusch's claims is Jona…
I personally believe FTL is likely impossible so I think the only realistic hypothesis is if we encounter aliens, that they're von Neumann drones on the vanguard edge of a colonization wave from an alien race that's been doing it for millions of years.
If we survive for long enough as a species, either we'll meet races in this manner or we'll be the ones doing it.
For the record I still only assign a fairly low probability that this is what is happening, it's more likely that UAPs are craft from terrestrial origin.