Quite like your explanations… fills in a few details of how I saw the scene! And you're reminding me particularly of the retorts Sherlock and John give as they're exiting the building (and hilariously fun moment to watch). 'Undercover' "Shezza" could have ducked his head back down when he saw John in there, but probably figured 'oh, hey, there's John! I've been secretly in here long enough, may as well leave with my buddy now and get noticed for the headlines I need to attract CAM's attention' (if that was, indeed, his intention). He irritably tries to explain it off as they storm out, saying 'I'm undercover!' John says 'No you're not!' to which he retorts dramatically 'Well I'm not NOW!' since he wasn't even trying to be so at that point.
(But yeah… even scruffed up, and in the midst of druggies, they really wouldn't think 'that looks like Sherlock'?)