Should you encounter this issue (for example after you imported a list into an existing list), you will find that you are not able to set the DefaultView property of the view to false or rather it will have no effect. The defaultview property remains true for the view you just updated.
Instead you should update the view you want to keep as default view. By setting the defaultview to true and updating both the view and the list.
SharePoint will correct the other views accordingly (and you won’t see your list multiple times in the site contents anymore).