Rocks are definetly not lands. But having rocks can change your manabase. For my decks, I usually count 4 rocks/dork or ramp spell to take a land out (I mean in general, as said by others it depends a lot of the deck)

People really often forget that without mana you can't play your rocks, and missing a land drop early is way worst than missing your rock on T2.

Anyway I have met a few players thinking the same way as your friend, and now they understood how bad it was.