Other possibilities can't be ruled out:
- Him being humble.
- He did land on the moon but (like Griffin pointed out) the broadcasted footage could have been a little different from how he experienced it exactly. Maybe he decided not to let these minor details bother him and instead let people be inspired by the event.
- There's really not much you can talk about a ball of rock...
- ...
Also, what if the Russians (and other countries) landed on the Moon afterwards and showed the Moon to be completely different? Surely the Americans knew they could not cover up something this big forever? I think they did land on the Moon.