I flew EWR to SFO on 5/2 and got to the gate early so the 7 am flight hadn't left yet (same gate too). I asked to go standby and made it on however there was someone in my seat. Well he got upgraded to first thanks to me.
On the return the following Wed I went standby for the earlier flight and got the exit row with no one next to me which was really nice.
I don't think he was upgraded thanks to you. I think he was upgraded, therefore freeing one seat for you.