This tweet is being blown out of proportions by assumptions. Yours is fine
So, I'll throw down a few moar. For plausible deniability.
1) POTUS could be referring to the store owners who are forced to retaliate to protect themselves. Something he'd be trying to prevent with the NG.
2) Amidst the absolute chaos, people undoubtedly be worried about their families. Increasing the risk of people shooting others out of self-preservation or simply by accident. Again, something NG would try it's best to prevent.
3) Shooting could actually mean a camera. As in high tech surveillance being used to identify looters, unruly, etc. (Although the masks sure help conceal, but hope you get the point. Reasonable doubt)
4) He could be talking about something else entirely. This could be a direct message to a specific person and/or target to warn them, once the damage of property in our Country was destroyed, this is no longer a "silent war", and the gloves are now coming off, fo' real.
I'm sure there's moar I'll think of, but just a few that crossed my mind.