It cannot be.

Leftism is not synonymous with forward thinking, nor synonymous with being open minded. Leftism is about worker ownership of the Means of Production.

Liberal, again, is focused on the Enlightenment philosophy Liberalism, which is characterized by espousing individual liberty and private property rights. It focuses on things like being open-minded and forward-thinking, like you've said, but you're misattributing that to leftism.

You've also been incorrectly saying Americans miscategorize the term into a right-wing term. It's the opposite, conservative fascists see liberals, who are still right-wingers, as leftists, due to the Overton Window. Liberals are still right-wing, and still espouse support for Capitalism.