You probably need to listen to more of Watts, Cold Steel. He didn't believe in a Christian God per se, although he did formally train as a priest as a young man but espoused the Chinese system.
He's just pointing out the absurdity of saying that one must follow either Jesus or Mohammed or Buddha or whatever, as its impossible to objectively say which one is right. Everyone reflects the bias derived from their own culture and religious milieu, as your very post demonstrates, no disrespect. It's impossible to say who Jesus really was or whether he or Mohammed performed real miracles or whatever.
So ultimately he's saying that what matters is the underlying message across all of them that we have a divine spark within us that we can tap into, but it can't be discovered through talking and dogma. 'God' can only be found from going inside oneself, in silence, which is the essence of all Eastern religious philosophy.
This makes sense Biblically when you consider that even the Bible teaches we are created in God's 'image'. That idea is common across all religions. So Eastern religion is basically just saying that 'God' can only be found by going inside oneself in meditative silence and understanding what that 'image' is, what that divine blueprint is that we all share, and conforming more closely to it.
That's what Watts means by anyone becoming like God and becoming one of God's 'sons'.