Is this the first time we can see N64 version so clearly and not in a off-screen video? This looks good, although zombies are too much like RE2 zombies geometry wise (wouldn't surprise me if those were the same models, only retextured).
RE Zero already used pan and zoom technique so that might be that. Looking at comparisons between the original and HD remaster you can see that those isn't just higher resolution original backgrounds. There are some details here and there added.
Also, good god is this game gorgeous.
My only guess is that they had higher resolution renders of the backgrounds, unlike REmake in which they had to just pull the images from the disc. They clearly still don't have the original 3D models tho to re-render as they're still doing the pan and zoom technique.
RE Zero already used pan and zoom technique so that might be that. Looking at comparisons between the original and HD remaster you can see that those isn't just higher resolution original backgrounds. There are some details here and there added.
Also, good god is this game gorgeous.