Ideally API key shouldn't contain anything regarding the account or any info right? it's meant to be an opaque string, is what I found in most of the other articles I read. Please do let me know if I am wrong about this assumption

JWT operates on a different principle; the user's private key (API key) never leaves the user's device. Instead, the stated "role" and other JSON data are signed with the servers pubkey, then verified by the server using its master key, granting the permissions that role allows.

Look at the JWT standard, it usually contains things like claims, roles, user ids, etc.