The aliens were baffled. They had discovered all kinds of strange and wonderful things about this planet, but this was the first time they had ever come across something that didn't exist.
They had been investigating the phenomenon of humans using what they called "USB to Firewire cables" in order to connect various devices, but try as they might, they could not find a single one of these cables anywhere.
After a thorough search of the planet, they came to the conclusion that there must not be such a thing as a USB to Firewire cable. The humans must be using some other kind of technology that the aliens were not aware of.
The aliens were baffled, but ultimately decided to leave the humans to their mystery and went on their way.