Yeah the contributors must have transferred ownership to the project. It might not need to be a signed contract though, at least in my jurisdiction it's possibl

Yeah the contributors must have transferred ownership to the project. It might not need to be a signed contract though, at least in my jurisdiction it's possible to agree implicitly if there's a notice about it. If not then whoever wrote it owns it - each individual piece of code; and it is the moment to call a lawyer.