The information you found on the origin of Mackinder appears to be accurate. It stems from Black's The Surnames of Scotland where you'll find it listed under Macindeor with the meaning 'son of the pilgrim'. Some of this information is replicated at
http://www.surnamedb.com/Surname/mackinder. The 'pilgrim' part appears alone in the surname Dewar (see
http://www.surnamedb.com/Surname/dewar).