Research suggests that women, more than men, are more likely to discern whether or not a couple is romantically involved or not. this is because women are more skilled at reading emotional cues

The answer is "Women are more skilled at reading NON VERBAL emotional cues."  Women in general have the uncanny ability to read body and facial language than men.  They are more attuned to reading meaning in simple hand gestures or eye contact.  Women are also sensitive for people's body language in relation to the opposite sex.