Both. The police certainly have culpability for being willing to send armed thugs anywhere to bust down doors and start shooting based on nothing but an anonymous phone call. Swatting wouldn't exist without America's militant police culture.
>Or when a racist calls 911 to report "suspicious activity" on a black person not doing anything that can reasonably construed as illegal or suspicious, and he ends up getting shot by the police?
Again, both. The police are always, and obviously, at fault for pulling the trigger on someone who doesn't pose an obvious threat. The instigation is the fault of one party, but the escalation is the fault of the system.
I'm not saying the person who posted the picture isn't at fault, obviously they have some culpability, and I'm not justifying it either. It's just odd that the employer is never considered to have any agency or responsibility in these discussions. The decision to fire the employee was entirely that of their employer. Presumably when they sat the employee down and asked for his side of the story, they weren't satisfied with "I was just cracking my knuckles." They could have taken one look at the photo and decided it was nonsense, but they decided to do an "internal investigation", suspension and eventual termination. No one made them. No one put a gun to their head.