This is a weird one and a first for me.
I was completely alone! Nobody was around it's hard to walk on that bridge and not make noise or for one board to creek from a human foot. The light makes some weird movements under the bridge almost like it's watching me. Again I never saw this light at any point while reeling in the fish or at any other point during the night. I was on the lake from 9pm to 1am I saw it on the bridge for a split second but thought I was seeing things until I saw the video when I went to Edit.
*Note, I don't think its a reflection because it clearly moves on it's own.
I chalk it up to it being one of those random nights on the water where you never know what's going to happen.