This doesn't seem like a good outcome. I bump that stupid thumbs up by accident far too often, to think that could constitute a contractual agreement is mind boggling.
Yes. A written contract should require a legal signature, be it a written signature or an electronic signature. Replying 'looks good to me' (or hitting thumbs up) over a text message etc should not be considered a legally binding contract, especially when you are talking about big ticket items such as multiple-tens-of-thousands of dollars in produce.
In any rate, once old mate sent the thumbs up, they should have exchanged actual contract documents.
This is why contract laws exist and shouldn't be eroded with nonsense like this.
Reading the case[1], there's relevant background specific to the circumstances. The judge notes the two parties had demonstrated a long history of executing contracts and doing business in this manner.
Most of the other comments here (at least at the moment) seem to have missed this nuance. The earlier HN post linked by OP mgbmtl has more interesting discussion: https://news.ycombinator.com/item?id=36618977
Give me a million dollars. Thumbs up emoji.
Now you're in for a million dollars.