Btw, you said "stress-tested"? Did you use that post by vapourminer while giving your bot a shot on that?
No, I'm just joking. The bot sent a notification to everyone because of a mistake I made. But looking at the bright side, at least none of the notifications failed.

I'll be writing some tests to avoid stuff like this happening again in the future.
edit: If anyone is curious about why this happened...
The bot checks the post for any mention of your username. If nothing is found, it checks for any of your "alternative usernames". If you didn't have any, the value would be "null".
For some reason, instead of just not passing anything to the check (null value), it literally passed
null and without any other rule, so it matched for the post everyone got notified about because it contained
nullius on it. Simple yet big mistake.