> No, it makes his mom the account owner.
Which makes the phone numbers under her account hers.
> Just because I pay the bill for mine and my wife’s phones doesn’t mean her number is actually my number.
It absolutely does mean that her number is actually your number. That you choose to share it with her doesn't change that; you can revoke that sharing at any time, or even cancel the line entirely.
(And of course, if both of you jointly own the account, then the numbers therein would simultaneously belong to both of you.)
> Imagine operating a company and the CEO isn’t the one paying the phone bill, it’s the accountant, and you claimed that it’s not the CEO’s phone number, it’s actually the accountant’s, but it’s shared with the CEO.
Is the phone bill under the accountant's name and paid from the accountant's personal bank account in this hypothetical? Or is it under her employer's name, and paid from her employer's bank account? The answer to that question determines the owner of the CEO's phone number, and in neither case is the CEO himself personally the owner of that number.
> The number is assigned to a person on the account which has nothing to do with who pays the bill.
And if that assigned person was the son then it would've been the son's name that Google pulled instead of his mother's, and Google's ignorance of its own advice would've gone unnoticed.