You would be surprised at how awful people are at shooting if they haven't put 100s of rounds down range on target.
I've trained people with the pistol and sometimes they've only shot a few rounds off, ever. It's one thing to be in close proximity (like a headshot to the back when the victim is on the ground already), but another to be 10-15 feet away. You have to account for stance, bracing, breathing, trigger squeeze, and recoil while emptying a magazine that can throw a round off even 1 inch if you're good, which is still a miss. In a fast-paced environment, you're shooting as quickly as you can and need to focus on all of those things, but if you let emotions get to you, like the fear of death yourself, they can be easily skipped and result in missed shots.
I can believe it as being realistic with 1 and maybe up to 3 people missing, but 10 is statistically over the top.