[nine_k]

I would suspect it's some average of many points that the control systems try to track, because the rocket is not a point, and the press wants to quote a single easy number.

I'd expect that the rocket has a ton of sensors, and a ton of passive and semi-active tracking devices all over the body.

E.g. I'd put a bunch of NFC-type responders in a number of key positions, responding at different frequencies. Then a typical sweeping-frequency radar pulse would activate them all, and the response time and the Doppler shift would tell about positions and speeds of many points on the rocket. I'd do a similar thing with reflectors and IR/optical tracking.

All these points should follow some reasonable trajectory for some point the top of the rocket, near the chopsticks, would move towards some desired catch location point. Probably this motion is where "with precision of whatever cm" relates to.