I think it's kinda pointless speculating, and even if there was more to it, the family (the parents specifically) might not even know.
I think you're getting too hung up on the "gang member" stuff. I'm not saying that's impossible, but there's a ton of gun violence happening now that's not random, but not "gang retaliation" either. A lot of times it's just friction between people that know each other in school or whatever.
Honestly, the most likely scenario (because this shit has happened twice at malls in my area over the past couple years) is that somehow there was shit talking with another group in the mall. And what used to be just kids talking shit and moving on now becomes one group following the other outside and opening fire. Which is a sad thing that it's where we are. But like I said, happened twice at 2 different malls near me. One was two groups of friends that knew each other and there was just one kid from each group that had an issue with each other (over a girl I think). Not gang members, just kids who don't know that real life isn't a movie and you don't settle shit with a shootout in a mall parking lot. The other one was 2 groups that didn't even know each other. I think the one "group" was just two guys and the other was a bigger group. Somehow there was shit talking and when the bigger group followed the two guys outside, one of the two opened fire.
Anyway, the point is we don't know and may not ever know. But kids getting shot sucks.