Info about who was polled is here:
http://www.cbsnews.com/8301-250_162-20125251/cbs-news-nyt-poll-10-25-11/
You are correct. The poll results with Cain having 25% percent are only from Republican primary voters. At the link they list out a little more info about sub-groups, but not everything.
I don't mind people pointing out details that the rest of us might not notice, but it bothers me when people start making stuff up. It seems to happen more more frequently.