Co-author responds to email by mistake cc'ing the EiC I (first author) received a decision on a manuscript recently (minor revision). All my co-authors were cc'ed in the decision email and some of them replied to the decision email saying "congratulations" to me while cc'ing the other co-authors. 

One of them accidentally cc'ed the Editor-in-Chief (EiC) of the journal!!! Actually, his reply was to the EiC of the journal with me in the cc. I think this horrible as formally the paper is still pending minor revision before publication. 

How should I react? Should I just ignore this or send an email to the EiC apologizing for the misdirected email of this co-author? I do not want to overreact but this got me anxious as I have been eager for this paper to get accepted.
I think you can safely ignore it. I don't see how or why the editor would suddenly disfavor your paper because of something like this. They seem to think your paper is worthy of publication and they want to publish such papers, not get upset about small communication glitches. 

And, of course, people often get cc'd on emails they shouldn't see, causing minor embarrassment. And I think that it is only that here: minor embarrassment. 

Let it go. Someone got a chuckle out of it perhaps, but there isn't any reason for them to take out the big hammer.