We're up to 5 deaths now.

Not to mention those that will result from COVID branching out from this event. Which - while less related - when considering the actions of the instigator are certainly notable.

DC has a ton of security, and it's basically only legal for them to possess the guns. Carrying guns openly in this area would lead to a quick arrest.

So - I think you're right that there was a lot of luck, but also there was a lot of preparation.