For me, I can only assume it's "violence that's prolonged and zoomed in on"
Like, for your scene -- someone's arm got ripped off and blood is gushing. Even though it's explicitly shown, the whole blood gushing from the actual arm is omitted.
If someone were to try and make it "shocking", they would probably have two-three panels zooming in on the ripped flesh, the pumping blood, and any other gore that's there, making the readers look longer than they probably should.
I think that's what they're talking about.
Or if you have detectives find a dead body that's been mangled -- "shocking" would be to focus entirely on the gore, maybe having different, zoomed-in angles to display it. The detectives are talking, but we never see them. We just see their dialogue over the gore.
This can be omitted by showing a silhouetted slumped figure, some blood splattered here or there, and actually seeing the reactions of the characters viewing it.
It's always a question of "should this really take several panels to show?"
Though, this is only my assumption (a good one, but still an assumption), so you might do better at going directly to a staff member and having them elaborate. Even when using your best judgement, having another pair of eyes to see can definitely help!