Wow this article on this subject has the least info. And the judge did not rule that it is always the case that a thumbs up would be binding, just that the context in this case it was.
The other party sent over the contract with he text: “Please confirm flax contract.” They then responded with thumbs up.
3 times prior to this, this exact same exchange happened. In each of these times the farmer replied with “Looks good,” “Ok” and “Yup.”. After which in all 3 instances the farmer then delivered the flax.
In this particular case the farmer replied with thumbs up. Then after 3 months the price of flax skyrocketed. And of course the farmer now wants a better price.
In this case the three prior contracts being agreed to with only a “Looks good,” “Ok” and “Yup.” and then being delivered seem to point that a thumbs up is pretty much along those lines.
Oh here is a version of the article that has a little more detail: