This plus a large network of amateur and professional astronomers who would almost certainly see any kind of craft coming towards the Earth and especially into the atmosphere. It could be that aliens came back before this was common and kind of ... hung around? Undetected. I don't buy it.
They almost certainly exist. But they are not here.
I remember the big floppy disks that were actually floppy. But the standard floppy disks were way more common and even they were on their way out