Added Second Menu but its taking over the wrong spot.

I registered a second nav menu in my functions file and added this to the location where I want the menu

<?php
                $args = array(
                  'menu'       => 'markets-nav',
                  'menu_class' => 'sidebar-nav',
                  'container'  => 'false'
                  );

                wp_nav_menu( $args );

              ?>

Now when I go into admin area the menu is there and when I add a page to it this menu shows up in the sidebar where I want it but it also replaces the header menu. Can someone explain what’s happening please?