This has happenned to me.
I was standing at an intersection waiting for the lights to turn when out of nowhere someone with a woman's voice complimented my handbag (which, truth be told, was actually very nice). When I turned to look, it was an actual woman. Funnily enough another friend going to the same place I was going was standing there as well. I mentioned mentioned to him after the fact how strange it was to have a woman just come out with a compliment to a stranger and how that simply does not happen when one is presenting as a male. After a while, it occurred to me the lady probably just wanted to hear my voice to figure out my gender. I got a quiet chuckle from that.
Whether I'd approach another CDer or not is a more complicated question. It depends on the where, how we are both presenting and the venue generally.
If I did spot a CDer, I would probably observe them for a bit to see how comfortable they looked to decide whether to approach or not. I have never had that happen, though.