Aluminum oxidizes and the mechanical connections degrade with time. They make special grease to isolate it from air and this is generally successful. It sounds like one of your connections wasn't adequately greased and developed a poor connection that heated up. Poor connections are like resistors that heat up. Thermography is done in industrial applications looking for poor connections.
The good news is that that your issue never burned down your house. Others haven't always been so lucky.
Jerry