A magic rock by some likely 100,000+ year more advanced civilization. Story wise however they could have been visiting the Grand Cannon as neither the protagonist or antagonist had access to magic. You could do the same thing with the rock saying releasing the Nanite cloud and nothing changes.
As far as 2001 is concerned it’s basicly highly advanced Starfish Aliens. https://tvtropes.org/pmwiki/pmwiki.php/Main/StarfishAliens Which seems like the most likely contact with extraterrestrials we will see. Motivation and reasoning are not going to be obvious, is this some major effort on part of their civilization or some 6th graders high school science project we just don’t know.
Again though, the Aliens are mostly irrelevant, it’s HAL human relations that’s driving things.
