Grusch doesn't know anything, he only repeats what he's been told, and what he's been told comes from the same group of Skinwalker Ranch/UFO grifters that have been blowing smoke up the backsides of Schumer and other credulous dupes for years. There is no reason to believe aliens are real in this scenario, or that whatever goes on in private briefings involves "real evidence" of such, as opposed to just passing on more nonsense that happens to be classified (like a lot of the already debunked UAP videos.)

Just because someone says something under oath, doesn't mean it's true. Just because someone says something in a SCIF, doesn't mean it's true. Just because a video seems to show a weird light or an orb or a triangle and the government says it hasn't been tampered with, doesn't mean the government is admitting that it shows proof of actual extraterrestrial craft.

The scenario presented in TFA is the simplest explanation that makes the most sense, even more so than it all being a distraction or intentional psyop to fool the Chinese or Russians. Maybe at the core of everything, there is some exotic foreign drone activity the Navy wants people to feel free to report, but the stigma of "UFOs" has gotten in the way. I can see some of this being part of a campaign by the military to make the phenomenon credible for the sake of national security, but not because actual aliens are involved.