My experience is that the fuel gauge tends to be affected by the "miles remaining" value. ie The gauge is not a direct representation of where the tank float sits. So if I have driven the car very uneconomically (ie multiple cold starts, hilly terrain, in town, lots of tickover, like I stole it!) for half a tank of fuel such that the gauge is bang on half, and then drive the next 100 miles economically, then the gauge will go up.
So if the op drove spiritedly up a mountain pass and then sat at the top ticking over for 10 minutes, followed by mostly overrun driving going back down the mountain, then the gauge readings shown are what I would expect to see.