“Proudly powered by WordPress” is not footer from the Square theme. This is something else what you see, maybe you have plugin for mobile version of your site (which is not needed, because theme is responsive). Or you did not select Square theme in Themes menu.
It seems you are using Jet Pack plugin and activated the mobile theme. You need to disable this module for the theme to show its normal responsive. Please check this link for more reference https://jetpack.com/support/mobile-theme/