"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.