They are clear it is not a prequel, it started as one but they decided to make it it's own universe, so to speak. The only parallels to alien I believe will be that Scott did both
developed a separate story that precedes the events of Alien... is not directly connected to the films in the Alien franchise... takes place in the same universe
Well it is in the same universe. It is before Alien in that same universe. Although it is not directly connected to the Alien films it "shares 'strands of Alien's DNA, so to speak'".
Therefore I believe it is safe to say it is--as I stated before-- "an Alien prequel of some sort"