First of all, Android is not only used on phones, but also for other types of embedded devices. It's very normal that a company B would want to go to company A

First of all, Android is not only used on phones, but also for other types of embedded devices. It's very normal that a company B would want to go to company A, if A already have a lot of expertise in Android. For instance a POS manufacturer might want to collaborate with Sony or Samsung on an embedded device which uses Android internally (without the GApps & stuff), but Sony and Samsung are forbidden from dealing with B. Even Amazon would be happy to outsource some Android development to e.g. Samsung but they can't.