I don't think there's anything racist about that if it's an honest mistake the audience makes. Or did you mean to say the actual presenters announce them by the wrong name?
And yes, he means that people walk up to Randall and say "oh hey, Brian!" and vice versa. Really, really often. Sometimes repeatedly. They're different heights, they don't even look like each other at all. They're just usually the only two black guys there. It happens at more than just Ruby conferences...
a) They have never met the speaker personally.
b) http://en.wikipedia.org/wiki/Face_perception
It has --nothing-- to do with being racist.
Yes, this is "We met earlier in the day, I'm saying hello again." Or, like I said, a waiter that over the course of a multi-hour dinner and drinks, continually confuses the two. (EDIT: Whoops, when revising, I apparently deleted that story. I've seen this too.)
Furthermore, it doesn't happen with other people, at least not to the same degree. People even say "whoops, I confused you with the other black guy."
Who knows, perhaps they even have an advantage because people actually remember them. They only get their names mixed up sometimes - other people are simply forgotten completely. How often do you forget the name of people you have just been introduced to?