Yes the cop doesn't know where the gun is, Which is why he was telling him not to pull anything out.
Hindsight is all well a good but when you stop someone you don't know, Who has a gun and is a suspect in an armed robbery case and starts reaching for something unknown and you don't know the location of the weapon, I'd say you'd be spooked too.
Mistakes were made both ends, Sadly this time it ended in death.
People are unpredictable. Simply informing the officer doesn't mean there is zero chance of him actually using it.
Then I'd say he shouldn't be a cop in the first place if he gets spooked so easily.
He literally shot him merely seconds after Philando informed the officer that he had a gun, and again the officer did not visibly see or know where the gun was. For all he knew, Philando was probably just putting his wallet back in his pocket.
He was also in a car with his family, including his daughter and informed the officer, as he should, that he carries a weapon. People are unpredictable isn't a good excuse for someone to get shot.
There is a statistic on how police who were formerly war veterans are less trigger happy than police who go through standard training. Can you imagine soldiers being trigger happy in an enemy warzone because they are paranoid about the citizens carrying concealed weaponry?
It's just unacceptable and it's really both the cop's fault and the current standard of police in general. They need better training.