Protection Diode Position on Regulators
A diode on the output serves a different purpose than one on the input. So D1 here does make sense and is unrelated to if you put one on the input or not.
As you pointed out a diode on the input protects against reverse polarity when you hook up the power supply. In that sense it is a good idea. The D1 here serves the purpose, however, of protecting backfeeding into the Vout from your circuit, which also would damage your AP7333. Whether your circuit would actually cause such an effect or not depends on your circuit. If your circuit produced a negative voltage for whatever reason without the diode it would backfeed the AP7333 and blow it, with a diode it would be protected.
Ultimately if the diode is needed or just an extra precaution depends entirely on if your circuit has the potential to introduce a negative voltage or not. If the circuit this will be integrated into is unknown then the having the diode there is a &quot;better safe than sorry&quot; sort of deal.
Keep in mind negative voltages arent that uncommon, dual rail power supplies are very typical with op-amps and thus many circuits have the potential to introduce a negative voltage here.