was distracted. While they were on the beach I. found something interesting, he has a history of zoning out, so when he saw it he got distracted by it. When the Seventh Man called to K. to warn him I. couldn't hear him, because he was so distracted by whatever it was he was staring at. It wasn't The Seventh Man's fault that his friend got distracted at the wrong moment, it was just something that was inevitable.
On the other hand, the Seventh Man could have done something to possibly save both of them. If the Seventh Man hadn't of been so afraid of what he saw coming, he could have ran up to where K. was and gotten his attention by pulling on him or something like that, even though K. was in a trance by something the seventh man still could have saved him. Then again if The Seventh Man would have ran to save K. he would have been risking his own life, and i don't think that many of us in that sudden moment would stop to think about running up to save your friend when your own life is at risk, would