ConcreteVitamin wrote: and am wondering if it's a good habit.
Agreed it is different. But that is STYLE. His style.
Even in the above still photo, you can see him dropping his arm to create a pivot point for the board to follow around. Like a Moto-GP racer putting down a knee on the tarmac. So it's not that static.
All my comments/observations and teaching of basic forms go out the window once you get to a certain stage. There was this Uncle at Waikiki that surfed with both hands clasps behind his back above his waist. That's the way he surfed. Now if he was falling off and wasting sections, we'd probably say he surfs like a kook, but no, he surfed really well.
Is it a good habit to have a "frozen", static front arm, I would say no it's not good. But if you can rip the tops off waves and land tail 360's with a finger in your nose or in a stink bug stance, then it's all good.