Even if the appointment were simply a majority of the board, that in and of itself raises bizarre questions. Why is a CEO appointed only on a 3-3 (or 4-2) vote? Usually you would want unanimity in important things like this.
This certainly opens up a lot of questions.
I'm going to be simultaneously cynical and optimistic here, but the story so far appears to be based on anonymous hearsay. Eich's appointment could perhaps be a smaller part of a big shakeup at Mozilla, board and all, that isn't predicated entirely on Eich.
Alternatively, and perhaps most realistically, the board members who voted for Eich may not have considered it a problem until they saw the backlash, both internally and externally. Both people and organizations alike can backtrack and develop new ideals based upon the reactions to their actions.
While we're doing hearsay though, I've heard no new CTO is on the cards which strikes me as odd.
Edit: I don't know how legit this is, but I just saw this on Twitter: https://twitter.com/TruthTellerMoz1/status/44967336620801228...