I'm not sanguine about the officer going in with his gun drawn, but under the situation described if he had to enter, having his gun drawn makes sense. The question is, did he need to enter, but that brief article has insufficient info to say for certain, tho it looks like he did.
The knife guy had just left a Costco (or something) and the security tried to stop him for reasons that are unclear. Knife guy put knife to his throat (this is all on video) and security gaurd backed off and the guy left the store. Security guy calls cops. The cops pull up in their car with the knife guy walking past them they start to get out as knife guy approaches, the driver is lunged at by knife guy, driver shoots him.
link to videoLike most of these, I don't know if the guy deserved to die, but I know what would have made him NOT dead.