This is where instagram/twitter theories start taking shape, none of those questions by themselves are really strong indicators of anything:
1: Why was nothing taken from the house?
Answer: Maybe money or drugs were taken, and not reported, maybe for the same answer as question 3, is that they just fired a gun, and murdered someone in a residential neighborhood, and the police were likely less than 15 minutes away
2. Why was Pop Smoke the only one killed?
Answer: Incidental, and too many scenarios, he was only one who challenged the suspects, or geographically the first person they encountered, because of the layout of the home, and where he happened to be
3. Why did they leave as soon as they killed Pop?
Answer: See #1
And here' something else, one shot to the torso, now there is no real all purpose version of a "targeted hit", but one to the torso could be anything, if it was multiple head shots, or obviously the two to the head, one to the chest (which would likely be uncommon here), you can assume death was intentional, rather than circumstantial.