Have you not seen the dashcam footage, or are you just lying? I will give you this, if it was a lie, you managed it so confidently that I had to look up the footage again to make sure I wasn't crazy.
To literally quote Castille moments before he was shot (in which there had been no yelling beforehand): "Sir, I do have to tell you that I have a firearm on me."
If you registered that as yelling "I have a gun!", then you are blinded by partisanship beyond hope.