Around the 51 minute mark... Alex - "Are you against the idea that there are objects from other planets that are flying here and that have intelligent beings inside of their craft... Are you willing to entertain the idea that that is an aspect of this phenomenon and that it's real in the sense that, in the same way stealth bombers are real that that's real?"
First, if a mechanical object appeared to folks on the surface of Earth which these folks experienced as technology "doing things" they have no knowledge of anything created by some amongst the general "surface of Earth born," "run of the mill," "publicly known," human race that could be capable of doing, the possibilities of the object's origin are many.
The question Alex asked could have been narrowed down a bit too, for example... "planets from distant star systems" because by not doing this, if it came from the Moon for example (which is another planet), that is not the same as some planet revolving around Sirius A for example, right? Much less a planet of another galaxy, right? Most believe it is not beyond current human technological capability to create a mechanical object and send it to the moon, but most are pretty certain humans (other than Ben Rich and friends) can't get a mechanical object (whether manned or not) to a planet revolving around Sirius A (and especially not a planet in another galaxy) right now.
What point am I driving at? The complexity of "aspects of the Phenomenon" really emphasizes the importance of bringing forth specifics in questions to folks like Marty IMO.
And now for a comment as to Marty's immediate response... Marty - "... [this] requires a rather complex explanation. And I'll preface it by saying, even the most unlikely explanation has as much validity as any other... in other words, it could be the most unlikely thing that could be behind this and it doesn't mean it's not that..."
So, what Alex got right in his question was the clear insinuation there's more than one "aspect" to "The Phenomenon" (as some insiders refer to it as while also emphasizing there are many aspects to it), Marty (unfortunately IMO) not only doesn't acknowledge there's the possibility there are more than one aspect (likely many, IMO) but, in his statement, it is almost as if he is transmitting a belief parameter (while never ever sharing the heart of what he believes (at least up to this point in the video}) that there's only one aspect thus one explanation to it all.
The greatest barrier to getting beyond the mystery is the inability for people who are in discussion a.) bring important detail into their questions/statements and b.) believe there's only one aspect and hold no real open mindedness there's possibly more than one, perhaps even many.
Thankfully (though only later in the video) - more aspects are covered by both Alex and Marty.