I am also not an expert, but America drastically increased farm subsidies a few years ago ahead of the Doho Round which is why the Mexico WTO meetings fell apart in acrimony.
This may be an olive branch or a fig leaf or a negotiating strategy. Offer to cut subsidies knowing full well that the French under CAP will not allow the EU to cut theirs, therefore making the EU look like the bad guys. By the way, the UK wants a cut in EU ag subsidies in return for scrapping their own EU rebate, which France wants it to do. Therefore, the US is just supporting the UK over France on this issue.
However, cutting subsidies might jump start the Doho round again as developing nations have insisted cuts by rich countries were necessary in order to liberalize other services sectors.
Regional development aid, not tied to production, would be in any case more suitable as a policy tool. But, we are a long way from an informal announcement to an actual agreement. I am sure many in Congress would look to protect their own constituent's special interests whether it is rice, cotton or corn?
In any case, a step in the right direction to be sure. Less pork in the US and more bread on the table of developing nations.

The organized state is a wonderful invention whereby everyone can live at someone else's expense.