What are the different grounds on a PCB?
It's suggesting that there is a "star-point" that "power ground" and "feedback/control ground" use as their points of reference to 0V. Anything that should/must connect to power ground i.e. input decoupling caps, output decoupling caps and main ground on the chip should be separate from ground on the feedback potential divider (not used on your design). These two separate grounds should make just one connection to each other and this is called the "star-point".

This ensures that load currents and input currents (that might create millivolts of volt drop on their track) do not influence the voltage that the feedback resistor network measures. If these currents did influence the feedback resistors, then you can expect a noisy output and possible instability.

The "star-point" is, by default, right at the main 0V connection for the chip.

For buck regulators (using a fly-back diode), this diode should be naturally on the power ground and NOT connected to the control ground. Several other pins may need to use the control ground and these include, soft-start input capacitors, oscillator resistor and capacitors and incidental digital inputs (such as external switching clock if used).