First, kudos for using "tazer", which is the word for such a device.
"Taser" is a brand name.
If it was indeed tazer vs gun confusion, this points to....
1) Poor training
2) Bad tazer design.
Consider....
When a cop who carries both experiences a high stress situation,
& if the tazer looks, feels, & operates much like a handgun, then
confusion is made reasonably possible. If the cop does get confused,
this also suggests that training is inadequate.
I'd favor redesigning the tazer so that it functions reasonably like
the handgun, but has features to alert the user to a big difference,
eg, make the tazer entirely a bright color.