Ah, a chance to bring up my favorite theory/most probable explanation.
Technomancers are awakened. They cast, they suffer drain, they summon things, they lose abilities when they [email protected]#$ with their essence, they initiate, etc.
Magic responds to belief and perspective, per the lore. That's why we have different adepts and all the flavors of magicians. And there's billions of people that believe in the Matrix. It was bound to have some effect. Technomancers being magic fits the lore, fit the theme of the game "Magic meets Machine", and fits the mechanics. Also? Come on, the Otaku were introduced as cyber shamans, FFS....
Also, there's no better explanation. Aliens? Radically changes the game. AI? Ok, fine, but how? At this point in the meta story someone would have noticed a bunch of nanites building decks into people's brains. "Hey Bob, what the [email protected]#$ is THAT?!". Also, it kind of changes the game tone. Evolution? Doesn't work like that, at all.
CGL in their infinite wisdom (grumble) isn't telling us, so yeah, it's all headcannon, but it's headcannon that fits the lore, the mechanics, and the game theme.
And yes, if there are technos around summoning sprites 'n stuff, it introduces Spooky into the Matrix. It might not be all machine at this point, so you kind of have a valid point.
And now to head off common arguments:
"But Tony, you can't be Awakened and Emerged! The rules say so!" -> "Sure, but that's probably because you can't be a magician twice. Also, I'm old enough to remember when you couldn't be an adept AND a magician, and now we have mystic adepts."
"But table XYZ says it's so much harder to see Emerged than Awakened!" -> "It's new and weird and most people haven't seen emerged, so yeah."
"But metasapients can't be technos!" -> "Says who? Why not? We have emerged plants and animals, I'm sure we'll eventually have a technomancer naga."
And they never have a better explanation. Occam's Razor is on my side.