I almost always use two tie-in points. It is always nice to have a back up in case "stuff" happens.
I believe his TIP was in the other tree, therefore he would need something to stop him from swinging back to his tie in point. In this case, I believe his flipline was wrapped around the branch he was cutting to support his weight and stop him from swinging back.
If possible, a tie-in point (or another) in the tree he was taking the limb from, would have been safer. Red arrow in pic below shows possible TIP.
This extra TIP would have given him the benefit of better work positioning (no need to be tied into the branch he was cutting). Although it would take more time to set this up, this would have afforded him to work above and away from his cut. (Perhaps even limb walk out).
Usually an accident is a combination of errors.
Thanks Chad566 for sharing this with us. It takes courage to show your mistakes so others may learn from your "experience".
Glad your still with us.:msp_thumbup: