If you call 911 and request the police come help you, have you ever wondered why it may take so long for the cops to show up? They may show up too late possibly because you did not say the magic words when you called 911.
Cops respond to calls based on priority. If you say, “There’s someone with a gun!” (or knife or any deadly weapon). When cops hear a deadly weapon could be involved then they are typically forced to respond immediately but you had better be convincing and sure when you make this type claim in a 911 call.
If the cops show up and there is no deadly weapon involved you had better be able to plead convincingly that you thought you saw a deadly weapon being brandished by someone. Supposedly you are not doing anything illegal if you “thought” you saw a deadly weapon being brandished by someone but it will be up to the police officer at the scene to make the final judgment.