Unfortunately it isnt meant to make any sense. Its just bad writing. IF there was no intention of explaining the Jockey on lv426, why use the SAME SOLAR SYSTEM? Why have a xeno bursting out of a different SJ next door. Its just bad writing....either tie it in or dont. The hologram sequence is a wasted opportunity as well. They could have easily shown what the Engineers were doing to cause an infection and what they were running from. We are talking 30 seconds of CGI. I mean come on. You could have had a totally independant movie from Alien and shown that. That's the only thing that needed to be referenced. But instead they dont. They reference everything under sky except the most vital revelation. Lindelof.......i swear this guy is deliberately trying to mess up things.