I totally agree: Nothing is outside of your mind, though. Everything's just you, boo ;)
I wrote this article because those words are useless until you've already had the experience of their truth. Like with happiness, just telling someone a spiritual truth doesn't often help them to actively experience it.
Interbeing (which if memory serves is a term Thich Nhat Hanh uses often!) means everything is you, or can be you when you take it as a part of yourself (and love is to take something as a part of yourself.) When you put your full attention on what's before you, there's no attention left for the concept of self, and the Ego falls away. Bliss arises.
Our happiness is internal no matter where it seems to come from. The fixation on something "being a source of happiness" is a further conceptualization of happiness, rather than letting the experience arise out of mindful focus on what's before you. Fixating on "being my own source of happiness" is going to keep me from putting my focus on what's before me.
Not everyone is yet practiced enough at transmuting experiences of misery into experiences of happiness without changing the "external stimuli" present. As someone who only recently started being able to do this, after YEARS of practice, for the first several years of my spiritual practice, trying to be happy from within just fell flat and proved useless. Pretty words that aren't hollow, but when you're not practiced at the teaching, don't actually help a thing.
I like my awakening as pragmatic as possible. I've spent enough time being esoteric and reaching no one but those who already understand me. They're not the ones who need the lessons :)