I'm not sure if the storklets scared each other by accident. While the storks were growling (they only did it very briefly), they all looked to the left. I've watched the moment when they got up several times, but could not see any other bird flying by.
All storklets were frozen after growling, - for a bit more than two minutes. This seems very long, - for that they have "only" scared each other. Maybe that's normal, I don't know.
Some more pictures of the incident.
22:12:39 The left storklet growled ...
22:12:40 ... here the one on the right.
22:12:45 They are frozen.