The AI SDK being ported was first released in 2023, so it was almost certainly designed/architected by a person. "Vibe coding" wasn't a thing until 2025.

However, that person worked for Vercel, so be aware that the design is apt to be questionable. Another comment has already pointed out some of the core design flaws, as is emblematic of everything that comes out of Vecel.

But you may find it useful if you have to integrate into that ecosystem.