It was a teaser!
"Unfortunately I got stuck on the Earth for rather longer than I intended," said Ford. "I came for a week and got stuck for fifteen years."
"But how did you get there in the first place then?"
"Easy, I got a lift with a teaser."
"Er, what is ..."
"A teaser? Teasers are usually rich kids with nothing to do. They cruise around looking for planets which haven't made interstellar contact yet and buzz them."
"Buzz them?" Arthur began to feel that Ford was enjoying making life difficult for him.
"Yeah", said Ford, "they buzz them. They find some isolated spot with very few people around, then land right by some poor soul whom no one's ever going to believe and then strut up and down in front of him wearing silly antennae on their heads and making beep beep noises. Rather childish really." Ford leant back on the mattress with his hands behind his head and looked infuriatingly pleased with himself.