I don't think they're missing that at all. The cattle in question are eating feed (mainly corn) not grass.
Furthermore the grass in question likely wouldn't "decompose" like what I believe that's describing. It probably depends on where you're physically located, but in the north - grass grows for the duration of the season, until it eventually dries out in the fall to go dormant over the winter. I guess I haven't personally tracked that process but I would be very surprised if it's releasing methane in the same way that freshly cut grass left to decompose (via bacteria) would.
Furthermore the grass in question likely wouldn't "decompose" like what I believe that's describing. It probably depends on where you're physically located, but in the north - grass grows for the duration of the season, until it eventually dries out in the fall to go dormant over the winter. I guess I haven't personally tracked that process but I would be very surprised if it's releasing methane in the same way that freshly cut grass left to decompose (via bacteria) would.