Why is Kayn from Ionia?

He was born in Noxus but was raised by Zed since his 10s and fight for the Order of Shadows since. He found Rhaast in a noxian city called Vindor, even though Rhaast wasnt sealed there.

In the end, Kayn hates noxians and fights for Ionia.

More him taking Ionia as his home since he's Zed's butt buddy, similar to how Xin is Demacian but from Ionia.

He was ditched in Ionia after being drafted as a child soldier during the war

IDK, Why are you from Wisconsin?

Riven is also from Noxus but has since went into exile into Ionia and is more Ionian then Noxian

There are a lot of champs like this. The region identifier doesn't read like a birth certificate it's more about which region the champion identifies with or interact in more.

Other champs born in other regions: