Is san da fighting?

Close, but not quite.
The purpose of a fight is to defeat an opponent, win a bout, score points etc.
San da serves a different purpose...

Your aim is to attack and defend skilfully using aspects of the art that work for you.
There are two reasons for learning this:

1. To defend yourself against another martial artist
2. To assist family/friends who are being assaulted

With the pressure of unpredictability, you find out what you can pull off.