Go to: https://tradingeconomics.com/commodities and randomly click on different Agricultural commodities, and switch to a 5 year view.
So far every single one I looked at had spikes of this type. A lot of them were during COVID though, so maybe my argument isn't great. But a lot of them weren't.
And to answer your question: The farmer will benefit at least somewhat because it means 100% of his crop can get easily sold because everyone is desperate for supply. He won't get the full amount of the rise, but some part will go to him.
> some poor farmer somewhere is seeing a windfall?
Think about what that would mean. To get such a windfall also means the farmer is completely exposed to the risk when the price goes down. Instead farmers will typically sell a year in advance, they won't get the rise, but they are also shielded from a fall. You can't have one without the other.
One of the prime motivations for putting cell service in poor countries is to give farmers access to the commodities market. They can sell futures, backed by their crop, or buy crop insurance, etc.
If you want to help a poor farmer that's probably the best thing you can do: Make a way for them to access, and interact, with the commodities market for what they grow.