Seems like it should. It's not that big of a deal, but yesterday a player with the ally that does extra damage against giants drew the Zombie Giant as an opponent, so it mattered slightly (the Zombie Giant is pretty weak for us at this point in the adventure path).
I think Mike commented on this once... I think essentially it USED to be a giant, but it died and has deteriorated to such a point that it has lost all Giant traits. It's now essentially a rather large, slow, hulking undead bag. It's not strong enough anymore to hurt everyone at your location (typical Giant trait) but it is still massive enough to hurt you more if you let it (the discard from deck ability).
Unless there is an errata issued... let the cards speak for themselves. If it says it's a thing, it's that thing. If it doesn't say it's a thing, it's not that thing.
Good luck on your adventures!
Motrax
Hm, well in terms of the Pathfinder RPG (which isn't always supposed to translate directly, but whatever), undead usually overrides any other creature types. A hill giant zombie would be listed as Undead rather than Humanoid (Giant), for example.
Regular zombie doesn't have the human trait, right? It's basically the same thing.
Definitely not a giant any more. The card game tries to be procedural with its traits: If it doesn't get a template's power (in this case, "smash everyone"), it can't get that trait.
If I had that card to do over, I might've called it "Giant Zombie" to avoid the confusion (that is, no one thinks a Giant Snail is a Giant). But it's fine as is.