look I am not saying it is only an RPG but it is one of the many games out there between genres....
Heart containers at the same thing as HP in most RPGs, and the magic meter is still MP. Yes it is not entirely RPG but honestly you cannot deny that the zelda games do share many characteristics of an RPG right down to the storyline it follows.
video games are a little hard to define genres for.
But for comparison, let's look at super mario 64, he has health, but you never get more, it is life based, you only have so many lives, you collect coins but they restart level after level, and you collect stars to move through the game.
Zelday has health but it increases through the game, you get rupees and hold onto them to buy things to upgrade or restore your character in some way, and you normally end up collecting something to advance through the game like the stars in mario 64 but unlike mario 64 these items normally have a greater significance in the story, such as the three gems in OoT that unlock the master sword.
Zelda like many games is a partial RPG.
how about Ratchet and clank? That too has many things in it like an RPG, probably even more so since the guns level up, and your health grows, but it is still similar.