Xukong had seen Lin Mu collapse earlier, but reckoned it was simply due to the impact of the Chimeric Fiend God's name. He did know that Lin Mu would be affected by the Karma, but was willing to let him experience it.
'I was going to act if anything bad happened, but he managed to get through it on his own.' This was what Xukong had thought earlier.
He would have certainly known if Lin Mu was in trouble due to Karma and would have interfered. But to him, it looked like Lin Mu had managed to get through it all on his own.
While he looked exhausted and his breath was unstable, that was not something that threatened his life.
In fact, if that was all he rendered after bearing the Karma of hearing Chimeric God Fiend's name, it was an excellent result.
But once Xukong heard the details of all that Lin Mu had seen an experience, he understood that the situation was a lot different.