That is 100% a King. And to the person who asked if there's a fishable population, yes there is. I don't know many that make the trek, but I head out a handful of times each year to the dead centre of the lake. On each trip out we normally box one or two salmon mixed in with a bunch of lakers. I also take part each year in the DEC cold water offshore diary program. That king you caught came from one of two places most likely. On the Canadian side, there are several tribs with fairly substantial fall runs of naturally reproducing salmon. Pinks, coho, and kings are all in a select few Canadian tribs. Big creek, big otter, youngs, and tribs of the Grand river all have a natural run of salmon. The second possibility is a stray out of Huron. The bait has been in steady decline there and I don't doubt that the lakes abundant salmon are finding their way here to eat.
That is not an atlantic, although several have been caught on Erie and the upper Niagara river this year. Those atlantics have wandered down from the heavy stocking program all the way from Sault Ste. Marie. Again, that shows these fish will move miles and miles for the bait they want.
Given the temps right now, it is definitely strange that you caught that fish at that depth. I normally hit them over 150ft and down around the 90ft mark where the water dips below 50.