If he had used just one weapon with several high capacity mags, I MIGHT think it possible.
Juggling two different weapons of two very different calibers, well, that stretches credulity.
More likely, the cops said something offhand, and the technical idiots in the press twisted it into a good, flashy headline, facts be damned.
Why? Just means that two mags, not just one, are already loaded. It's actually faster because it's easier to drop one & grab another that's already loaded than to reload one that's empty.