This may be where I saw that bit of information. There are also people on the internet claiming that the story is false, so at this point I will put it in the ambiguous category.
http://www.thepostemail.com/2009/10/21/2nd-witness-to-obama-admission-in-keyes-vs-obama-2004-debate/
I remember hearing/seeing and of course many times reading. I believe it was on Youtube also. Has anyone contacted Keyes?