It was keeping a constant angle to the wind.
To do that it has to continually change the heading of the boat to keep the wind to heading angle constant.
This mode is great for passage making as the sails don't need constant attention.
The course is not constant, it varies with the wind direction.
If you have a constant heading or have a waypoint that the pilot is steering to, and the wind direction changes, you need to adjust the sails.....and sometimes you may not be able to and end up in irons or involuntarily gybing.