I read everywhere that lake trout in Lake Superior are only accessible to flyfishermen early in the spring when they are in the shallows eating spawning smelts. Then they go into deep water

A friend gave me a lake trout that he caught while trolling for rainbows in Lake Superior.
I emptied its stomach and it was full of adult mayflies and a few beetles.

Now this was a small trout of about 2 pounds. I wonder if lake trout reach a certain age and switch to eating other fish, but this one a least was feeding on the surface.