How do grizzly bears know that humans aren't food?

How do grizzly bears know that humans aren't food?

I mean, I've seen videos of them taking down elk and bison etc...

So if you get a chance to backpack in grizzly country, how do you rest easy in your tent knowing that the average hungry grizzly bear won't equate humans with food? And I don't mean the food humans bring with them, I mean how do they know that humans aren't food?!

Serious question!