It does look like a different speaker. I just sent an inquiry to the seller.
"Hi, I'm contacting you about the RBH C-770s you have on Craigslist? I noticed one of the 3 have 2 sets of binding posts and the other 2 only have one, suggesting different speakers. I might be interested, but am curious about that. It almost looks like a different speaker."
Sent him a text. Let's see what he says.