Ehh, reading the article makes it clear that the farmer fucked up.
Best case, he gave it a thumbs up to show he read it and then forgot to ever follow up or reject the contract. However it seems like he had previously accepted and executed contracts via text, which reduces this likelihood.
Worst case, he did the thumbs up to show he agreed to it, and now is trying to back out either because he can't make the deadline, or because the price of it has shot up.
Neither case is great for the farmer. Contracts can be made from whatever form - verbal contracts are perfectly acceptable, so I'm not sure why people are freaking out about this. If he had said "Agreed", or "yes" in response to the text then that would be taken as confirmation of the contract too.