This was my experience with Zeke, at first. Now I can tell the difference, he paces a little when he needs to go potty, he just stares at me (us) when he wants to just go out and sniff stuff.
As for the op ... how I got Zeke to ring the bells, when it was obvious he needed to go out to potty, I would take his paw and swipe the bells, give him a treat, and then take him out, another treat when he did his business, if he didn't "go" then no second treat. He eventually figured it out. Now he'll just go to the door, no bells, as mentioned, he paces when he really needs to go. I still give him a treat every time he does his thing outside, even if we're already out, haven't had an accident for a very long time.