Firebase A/B Test - same userId on different devices

Does Firebase A/B testing take into consideration user id which is set by FirebaseAnalytics.setUserId? Here is my use case:

1. John Doe opens the app
2. He signs in
3. FirebaseAnalytics.setUserId is called with johnDoeUserId
4. Remote config values are fetched -> he lands in VariantA
5. John Doe opens the app on a different device (same Google account)
6. He signs in
7. FirebaseAnalytics.setUserId is called with johnDoeUserId
8. Remote config values are fetched -> is it guaranteed that he is going to land in VariantA?

Does userId has any meaning for A/B test?

No, this is not guaranteed. The ID that will be used takes the device into account, so it is possible for the same user to be in two different variants across devices.