Just what holster is "appropriate" might be a matter of opinion. Of course, most news articles provide very little information; only that it was a "firearm" and that he had a "handgun" permit, so we can assume he didn't have a rifle or shotgun, but whether it was a revolver or a semi-auto, what size, model, caliber, what kind of "safety" etc. is anyone's guess.
Even law enforcement officers disagree on which holsters are "appropriate". Sig Sauer sells paddle holsters for their semi-auto handguns. I have one of them and I know of a police department whose officers carry them. However, you can find on the Internet where some idiot, practicing his quick draw using one, shot himself. So some police departments, including Dallas, now prohibit paddle holsters.
I'm not sure which holsters are always "appropriate" and which ones will guarantee that you can't shoot yourself using it.