Couple points.

Not catching a fish there does not equal no fish there, although for someone of your skill level it would be hard to imagine not catching fish if they are there. But the only way you will really know is to snorkel the hole or run a camera through it. To me it looks like a perfectly good spot for fish to hold in the winter. Maybe there is something in there that eats all the other fish, like one of those leg-long brownies waiting for a fly the size of a muskrat.

Water only gets "too cold" for trout when it becomes frozen solid. I have caught fish (and not one or two but hundreds over the years) out of pools that had ice shelves out from the edges, slush floating down the thalweg, and/or anchor ice on the rocks in the shallows. We have resident trout here in creeks that are frozen completely over, then covered with several feet of snow, for several months out of the year. They manage.

At cold temps oxygen is not going to be a problem unless there is some chemical reason it is being lost. There is enough surface area there to oxygenate the water.

Silt is not a deal breaker either. Lots of inverts use silt, and whatever is UPstream of that is providing food as well.

I would be looking upstream for answers. Effluent from a cattle operation, little rainbows in the water from some old dump site, acid runoff, or a warm spring that draws in fish from downriver. Maybe in March all the fish are up on spawning areas elsewhere in the river.

Let us know what you figure out. Cause that spot screams trout to me.