I think there are a number of things going on here:
I think much of what the article is dancing around the entire time is that most philosophers/philosophy departments do not think this other philosophy is good/worth teaching.
Philosophy departments do not teach the Bible, they do not teach Ayn Rand. Both have some barely tangential relation to philosophy but are not particularly deep so as to even be worth reading as far as philosophy goes. I think the authors are trying to force philosophy departments to make this tacit claim they have always made silently out loud -- that Confucius, say, is just not as deep as Kant or Hegel.
Also primarily the history of philosophy is a conversation. In order to understand Nietzsche/Kierkegaard, you need to put them in context as responses to Hegel. They use technical Hegelian terms to craft their theories and responses, which you need to spend time grokking before you can make sense of anything that follows. Why do we cover Descartes' cogito rather than the floating man? Well, partially because it is better (he wrote it second, after all). But more importantly because of the hundreds of years of conversation that follows it as a jumping off point, because of the hundreds of brilliant philosophers it allows you to read, now in-context.
And philosophy tends to define the framework that all intellectual activity in a culture takes place. If you're interested in new theories and ideas in psychology, look to philosophy about a century prior and you'll find every single one lined up and argued exhaustively. A lot of the work of philosophy is to understand and challenge the way our culture thinks about things. Mencius would be very relevant when you try to understand Chinese culture, not so much ours. So in this sense the authors are correct I think, that some part of philosophy has this end goal of understanding the history and future of western thought and culture, for which non-western thought is a tangential oddity.