To add some context. The farmer involved had previously agreed multiple other contracts with a thumbs up. In context it was obvious the thumbs up was intended as "I agree".
Courts recognising how language and communication is changing is completely normal. It's the same concept at the tick box+button press of online contracts. So long as both parties are aware of the terms, and accept them, that's all that counts. A signature is just the most formalised acceptance method.