The whole idea was that if the Auriga made it back to Earth, the aliens would get loose & run rampant like a plague. Although Johner's comments did seem a little out of place in that situation. Either he was trying to be witty in some strange, abstract way, or he was too simple minded to see the bigger picture of the creatures reaching Earth. Although in the end, the crash of the Auriga ended up causing a colossal amount of damage anyway, completely obliterating the city of Paris.
The fact that the crew of the Betty had been smuggling contraband & other illegal "goods", & could have been wanted criminals on Earth could've had something to do with Johner's reason for not wanting to go back.