When he was sure that Irvin couldn't escape, he removed the black silk around his head.
Once the black silk was removed, his unruly red hair bounced up and became free. His face was also revealed to Irvin.
Irvin's eyes widened in shock. He said, "How??"
He was shocked because he couldn't believe that Arthur was still alive and that Arthur possessed power that was at the second mortal coil.
The fact that Arthur had a power that was at the second mortal coil explained a lot of things. It explained how Arthur was able to survive the ambush. But it didn't explain why Arthur was affected by the ambush at all.
A cultivator at the second mortal coil is a giant beast in human form. If Arthur was really at the second mortal coil, he should have been rampaging through the horde of boars, not being pushed to the end of his life.
So Irvin had an answer for why Arthur survived, but he was still confused about a lot of things.