Why would it be arcane meta-magic? Poison is Dark and the Cure is Light. Teleport is Arcane, why wouldn't it's counter be it's opposite.
I think, for the same reason Nullify is Arcane and Metamagic: it's magic that effects magic. If it was the sort of thing involving stabbing, bludgeoning, or skewering, War would be the right school. Or if it was a big guy with a big shield wearing Lightning +2 armor, War would be the right school.
But it's a defense against teleporting, and yes teleport is Arcane magic, but antimagic is Arcane, too: Nullify and Jinx, as well as things like Mana Syphon. By giving Arcane metamagic, they made Arcane its own opposite.
Now, something themed like "Spiked Iron Boots to the Center of the Earth" might be war (or war+earth), so yeah, it depends somewhat how it's framed. But a personal Teleport Anchor Enchantment, or a zone Enchantment are almost certainly metamagic because they're magic changing magic, and that makes them Arcane. At least to my mind.
On the other hand, Armor Ward is Holy and War, so not all antimagic is Arcane. I could very well be surprised!