You know I had always assumed it was an oversized wyvern, but that wouldn't normally have that terror effect attached to it. My next thought was Vorax-Hul, but I don't think it is ever stated that he has bat-like wings later on. I thought this was an easy question, but I must say that I actually don't think I have a great answer for it right off.
It's been a while, but I recall having wyvern riders drop bombs, and a crush of terror at a gate as a dragon flies overhead and hits everyone with dragon fear, and then the wyvern riding knight crash near the PCs and pose an optional deadly threat.
I was under the impression that was indeed Vorax-Hûl from Chapter 9; it would make sense that the dragon which helped Ragesia conquer Gate Pass would take up residence in the clock tower. As far as the "bat-like wings" phrase, I think that was simply to impress upon the players the sheer exotic nature of dragons, since their characters would almost certainly never have seen one, at that early point in their careers. The wings looked like a bat's, because it's the only frame of reference they probably have (outside of any experience with the Ragesian military and their wyvern riders).