1. Gated community - The kid wasn't known to the security people
2. Security on patrol notices an "unknown" individual
3. Security stops to make inquiries (as they are paid to do)
4. Kid becomes belligerent and aggressive
5. Security doesn't fare well in the tussle and fears for their life
6. Kid gets shot
Did this happen? Haven't a clue, but it is a scenario that could lead to use of force.
My gut tells me something is amiss here but absent more details there isn't really much to talk seriously about.