This is from Riida's interview with Tetsuko Kuroyanagisan in Tetsuko no Heya aired February 13, 2009.
Tetsukosan mentioned that she and Jun actually saw each other before Ohno guested in the show. She said that when it was time to say goodbye (they saw each other somewhere), Jun approached her and said "Ohno's going to your show, please take care of him.". And she was like "this group's bond is really amazing! Imagine they know those details about their groupmates' personal schedules."
Apparently, Jun was the only one who knew. lol. (Or maybe the rest of Arashi know about each other's schedules... and it was Ohno who didn't!)
Anyways... Ohno said
"I think I'm not fit to be Arashi's leader. Maybe Jun should have been... I don't have any idea about their schedules!"