It's hard to know if this is a studio cash in decision... they know Prometheus got a lukewarm reception, perhaps they think sticking Alien in the title will be good for ticket sales...
After how they screwed the jockey origins (incomprehensible alien to bald dude) I don't think they could do more damage, so if this is a change in direction perhaps it is a good thing...
I guess we won't know until some plot details surface. Also saw that it's been reported as March 2016 release?