Warning shots imply that the armed citizen had time to retreat or find other means to deal with the situation. As in this case, the 91 year old man did receive wounds to his leg due to a ricochet from one of the "warning shots". As "armed citizens", we are not military nor law enforcement. There is no "department policy" or "rules of engagement" that we must follow prior to discharging our firearm in self defense. A good defense attorney could turn the situation around and argue that the victim now became the "aggressor" and held the BG at the scene against his will. This might not be a problem in the state of FL, but there are states where this may cause serious legal consequences.
Fortunately in this situation, everything turned out O.K. What I don't want to see is a member of the gun community encounter a similar situation and attempt to do as this 91 year old gentleman did, and end up finding themselves in jail.
General rule of thumb, if you're going to discharge your firearm towards the BG, be sure that you're doing so to "stop the threat". Notice I didn't use the "K" word, I simply stated that you shoot to "stop" the BG from causing harm to you or other innocents. Anything else could result in a loss of your RKBA.
gf