Good eye! It is made by Soleil (Itagaki's studio) and you're correct in assuming enemies aren't as aggressive in general; however, in this particular clip, the grenades the boss keeps tossing from off screen and the multiple group knockdowns/finishers here make them look more docile than they actually are. If I miss the gun counter at the beginning, or if I don't have enough meter to execute the gun takedown near the end, the encounter was gonna look much different.

The one enemy left near the end did not attack because I killed enough to trigger a cut scene. He comes after me after it ends.

In terms of difficulty, I'm playing on normal here, and I have died a lot so far, but this could be due to my general discomfort with aiming and gun-based combat in most games, so your milage may vary there. Also Hard difficulty is unlocked from the get-go, so the option is available.