The emoji is certainly problematic, but it wasn't the sole piece of evidence regarding the contract.
"The buyer, Kent Mickleborough, later spoke with Swift Current farmer Chris Achter on the phone and texted a picture of a contract to deliver the flax in November, adding 'please confirm flax contract.'"
If I've talked to you on the phone about the contract and then send the image with a request to confirm the flax contract, it's harder to argue that a thumbs-up only reflects receipt of the message instead of a confirmation, especially if no further response is sent by the recipient.