oh, I see, thanks Rezzahan for explaining

Artifact is a card type, it is not a creature type. Creature types are the subtypes of the card type "creature" (and "tribal"). The card type "artifact" has its own list of subtypes. An object's subtypes are listed after the dash on the type line. The changeling ability grants all creature types (see below) to the object if it is a creature or tribal. Here are the rules listing ALL creature types, and ALL artifact types, to date:

205.3g Artifacts have their own unique set of subtypes; these subtypes are called artifact types. The
artifact types are Attraction (see rule 717), Blood, Clue, Contraption, Equipment (see rule
301.5), Food, Fortification (see rule 301.6), Gold, Incubator, Map, Powerstone, Treasure, and
Vehicle (see rule 301.7).

205.3m Creatures and tribals share their lists of subtypes; these subtypes are called creature types.
The creature types are Advisor, Aetherborn, Alien, Ally, Angel, Antelope, Ape, Archer,
Archon, Army, Artificer, Assassin, Assembly-Worker, Astartes, Atog, Aurochs, Avatar, Azra,
Badger, Balloon, Barbarian, Bard, Basilisk, Bat, Bear, Beast, Beeble, Beholder, Berserker, Bird,
Blinkmoth, Boar, Bringer, Brushwagg, Camarid, Camel, Capybara, Caribou, Carrier, Cat,
Centaur, Cephalid, Child, Chimera, Citizen, Cleric, Clown, Cockatrice, Construct, Coward,
Crab, Crocodile, C’tan, Custodes, Cyberman, Cyclops, Dalek, Dauthi, Demigod, Demon,
Deserter, Detective, Devil, Dinosaur, Djinn, Doctor, Dog, Dragon, Drake, Dreadnought, Drone,
Druid, Dryad, Dwarf, Efreet, Egg, Elder, Eldrazi, Elemental, Elephant, Elf, Elk, Employee, Eye,
Faerie, Ferret, Fish, Flagbearer, Fox, Fractal, Frog, Fungus, Gamer, Gargoyle, Germ, Giant,
Gith, Gnoll, Gnome, Goat, Goblin, God, Golem, Gorgon, Graveborn, Gremlin, Griffin, Guest,
Hag, Halfling, Hamster, Harpy, Hellion, Hippo, Hippogriff, Homarid, Homunculus, Horror,
Horse, Human, Hydra, Hyena, Illusion, Imp, Incarnation, Inkling, Inquisitor, Insect, Jackal,
Jellyfish, Juggernaut, Kavu, Kirin, Kithkin, Knight, Kobold, Kor, Kraken, Lamia, Lammasu,
Leech, Leviathan, Lhurgoyf, Licid, Lizard, Manticore, Masticore, Mercenary, Merfolk,
Metathran, Minion, Minotaur, Mite, Mole, Monger, Mongoose, Monk, Monkey, Moonfolk,
Mouse, Mutant, Myr, Mystic, Naga, Nautilus, Necron, Nephilim, Nightmare, Nightstalker,
Ninja, Noble, Noggle, Nomad, Nymph, Octopus, Ogre, Ooze, Orb, Orc, Orgg, Otter, Ouphe,
Ox, Oyster, Pangolin, Peasant, Pegasus, Pentavite, Performer, Pest, Phelddagrif, Phoenix,
Phyrexian, Pilot, Pincher, Pirate, Plant, Praetor, Primarch, Prism, Processor, Rabbit, Raccoon,
Ranger, Rat, Rebel, Reflection, Rhino, Rigger, Robot, Rogue, Sable, Salamander, Samurai,
Sand, Saproling, Satyr, Scarecrow, Scientist, Scion, Scorpion, Scout, Sculpture, Serf, Serpent,
Servo, Shade, Shaman, Shapeshifter, Shark, Sheep, Siren, Skeleton, Slith, Sliver, Slug, Snail,
Snake, Soldier, Soltari, Spawn, Specter, Spellshaper, Sphinx, Spider, Spike, Spirit, Splinter,
Sponge, Squid, Squirrel, Starfish, Surrakar, Survivor, Tentacle, Tetravite, Thalakos, Thopter,
Thrull, Tiefling, Time Lord, Treefolk, Trilobite, Triskelavite, Troll, Turtle, Tyranid, Unicorn,
Vampire, Vedalken, Viashino, Volver, Wall, Walrus, Warlock, Warrior, Weird, Werewolf,
Whale, Wizard, Wolf, Wolverine, Wombat, Worm, Wraith, Wurm, Yeti, Zombie, and Zubera