Earlier quoted context omitted.
Weird analogy. Nonsensical from both physical standpoint (the only energy input when swinging is the person on the swing "pumping their legs"), and practical one (you usually sit down with the swing already at an angle and then kick off, so a good 50% of the arc/momentum is there from the setup ).
You clearly didn't read this. It's about rowing. Not being on a playground.
"Recall the pure joy of riding on a backyard swing: an easy cycle of motion, the momentum coming from the swing itself. The swing carries us; we do not force it. We pump our legs to drive our arc higher, but gravity does most of the work. We are not so much swinging as being swung."