Correct. Just "unweight" the seat. No need to stand up. Just lift enough weight off your butt to allow the seat to move under you if it has to. It's also a good strategy if you come up on a bump that catches you off guard, such as a bridge joint, because it also has the effect of additional suspension travel.
I almost hit a small animal this morning. Beaver, or racoon. It was dark. There was a car a couple seconds behind me, so I didn't brake hard. It looked like I might hit him, so I lifted my but, gripped the tank with my knees, and was ready to destroy that critter. Go lucky though. But it's the same strategy. I'm thankful that it is a natural reaction for me.
As I reflect on that situation, though, I realize that I was looking at the animal, and not at a clear path for me to take instead. (Object fixation)