Responses
It's not that yoga was entirely unknown back then. But Shaolin followed a different discipline all together. So they didn't get much overlap. Not to mention that modern yoga doesn't just incorporate ancient indian yoga practices, but also modern physical techniques.
Also in this setting it seems like different clans/schools practice their own distinctive and traditional martial arts for the most part. So at least before our MC started changing things, the monks would have likely seen it as something akin to heresy to practice the martial arts of "outsiders" instead.
There's a saying in pt-br that goes
"Why are you trying to teach the priest how to pray?"
Teaching yoga to shaolin monks seems like a wild thing to me. In murim they... Don't do yoga? Wild.