I should have been more clear. When I said that the heavies were posted at either end of the street, I didn't specify whether or not they were in vehicles, but with both Snow and Sammy potentially 'checking out' (by VR and astral) or engaged in studying something other than the surroundings, it is perfectly appropriate for Clem to be close to, if not in, the vehicle, providing you with security. Also considering that this is LA, the windows are open, and given Clem's enhancements and perception, you could have had what you would reasonable consider a low volume conversation and she could have been 5 meters away and leaning on a lamppost and gotten every single word.
In fact, let's assume that is what happened, for the sake of appearances. I don't see Snow as being someone who would intentionally have spoken of Clem without talking to her if she thought she could be heard.