Yes, that was a Black man in the original Alien suit.
Bolaji Badejo got into the suit by pure happenstance, like latest-white-starlet-found-at-an-eatery chance. In his case, a casting team member from the original film approached the Nigerian graphic-arts student at a London bar and put him in touch with Alien director Ridley Scott. The reason why Scott thought Badejo could work the costume (and won the role over Peter Mayhew, who played Chewbacca): Badejo stood at 7 feet 2 inches and had a “slender” “erect” frame which, being so long-limbed, could “give the illusion that a human couldn’t possibly be in the costume.” Stuntmen also got into it for certain scenes. (For more on how Badejo worked the suit. check this out.)