I think he's pointing out that when virtually anyone talks about the "line of flight" they're talking about the line of flight, not a point on the line of flight.
Here's a rule that a kid told Natalie.
Natalie had putted from on the putting green and hit a ball near the hole. The "helpful" player said the penalty was on the girl's ball who was hit, because it "got in the way of your ball" (to Natalie). 🙂
Actually, line of flight does come into play in determining the point of reference for deciding where to drop when a ball is lost or unplayable in a water hazard. The point on the line of flight where the ball last crossed the margin of the hazard is your reference point. Once that point is established, line of flight no longer figures into the process.
From the link you gave:
"The top 125 players from the FedExCup competition, after the Wyndham Championship, will be eligible to play in the first playoff event. In the event that one of those players is unable or chooses not to play, the field will be shortened and no alternates will be added."
So nobody outside the top 125 can play. Same for the rest of the events --- nobody outside the top 100, 70, or 30 plays in the next three, even if players withdraw.