Regarding the armed response unit, I imagine that they simply followed SOP, and that the 'weapons drawn' was part of the protocol for dealing with incidents where the presence of a firearm has been reported.
As I posted earlier, this is also the standard procedure for almost all police forces in the US, even when dealing with a member of the public who has a CCP and legally carries a gun, until the firearm has been secured.
Perhaps in the same way that placing a suspect in handcuffs when they are arrested is part of the standard process for UK police forces.