He meant something entirely different
Although it hasn’t happened in years, I have managed to receive free transportation at times in the past, by standing near a ditch and sticking my thumb in the air. Note carefully; one thumb. Because if I had used two hands, I could now be found in breach of trademark. As well as in violation of a number of sections in the Highway Act. Real trouble.
We have any number of gestures that have been around since men wore togas and kept their hair in place with olive branches. The big one, the one that signified a willingness to watch brutal death while out for an afternoon of state-run entertainment, involved signalling to “the umpire” that the other player was “outta there”. Or maybe not. Thumbs down versus thumbs up.
My short research this afternoon returned that this story is apocryphal. The actual signalling may have been much more complex, and included yelling rudelly in Latin. However, we have carried the gesture forward, and it has come to be a sign of approval if the thumb points up. Except, of course, in the Gulf, where it is abjectly rude. Americans did it to show things were OK and the locals used it in exactly the opposite sense. Mixed messages if ever there were any.
A famous movie review team adopted the up version to show satisfaction with a given movie, and the tradition carried on even after one of the team up and died. Now, there is a contractual dispute in play over trademark infringement. Only in America…
Meanwhile, the next time you decide to stand near a line of moving cars with one thumb stuck in the air, your message may be a) I want a ride b) I agree totally c) I hate your Imperialistic blasphemeous spirits and d) I intend to sue you, too. Any or all of the above. As for the next person in line; he meant something entirely different.