I'm absolutely in favor of the a cop's right to draw a weapon in a situation like this. Every cop I know (and that's a healthy number) will allow for an exchange on information to get a situation clarified -- but it is critical that they have "gun in hand".
And, for the record, I'd even give Ol Whirly a chance to provide his explanation. Well, I might accidentally "flinch" off a couple of well placed rounds . . . but I'd start out by giving him a chance.