I'm not a beaver guy but I'd presume that during heavy rains that stream is connected by surface water to a larger body of water...??? Maybe he could have swam up during a wet spell?

In spring, you’ll catch beaver where there is no beaver. I had one trying to make a go of it at the corner of our road and the highway this year.

the creek does not flow to the nearby river. Im in the Great basin, things dont always do what you expect. My best guess is it came from over the mountain where a similar creek that sheds off the same mountain off the opposing face comes closer to the river. Still had quite a distance and terrain to walk either way.