It is consistent but it may not be obviously consistent so I agree there is room for improvement there. The upper left back buttons are always to go to a differ

It is consistent but it may not be obviously consistent so I agree there is room for improvement there. The upper left back buttons are always to go to a different "screen" or function. The bottom back buttons are to navigate pages. The confusion with the browser comes simply from the fact that people mix a screen with a page because websites all look different. You're not going to a different screen within the app but you might assume so because you're going back to a different website.