Okay, but I recall Superman used much harder blue-screen trickery, and was earlier than Blade Runner. They had to key out a man with flapping cape and wind in hair.
Even if not keyed, the rear projection would have worked too. Doesn't matter I guess. I didn't realise 2001 had flat screens! Good pickup.
Interestingly enough, the screens in the film 2001 were all flat - because they were rear projection screens, with film or slides projected onto them.