Bears are one of the few animals beside us that are plantigrade. They walk on the same parts of their foot that we do. This is in comparison to a dog or cat or a ton of other species that walks on their toes.
I imagine people see bears are plantigrade and unconsciously realize something is up with that, but not what. I don’t think the bear is mimicking our stance, as standing up like that sometimes to look around is a bear thing already.