Epic says it was realtime. On Series X? I'm not sure, but running on real hardware,and realtime, and running on real hardware in realtime are 3 different things. Remember that Sony once showed a "running on PS3" trailer for Last Guardian that ran at a near flawless 30fps and looked better than anything else on the system, and only after the PS3 version was cancelled was it revealed that the game was only running at 15 fps and they played it back at double speed for the presentation.
Hellblade 2's trailer has a bunch of small scenes with very high details. It isn't beyond the realm of plausibility to me that those tightly packed scenes, with fixed camera angles, couldn't be rendered on Series X, or PS5 either. I think they will be able to get that quality in the characters in the real time cinematics at least, maybe not in gameplay. But the trailer wasn't gameplay, just a next gen showcase. There's very little gameplay in the Horizon 2 trailer either. Lots of in engine cinematics setting up the story, and a big turtle standing up, and some scenes of robots walking.