It's been a long time. All sort of things can influence the orbit of an otherwise straight line. Just a fraction of a degree can drastically change an orbit.
Plus, Weyland-Yutani may well have already had probes in the back yard of LV-426, to have picked up the original transmission and located its origin before anyone else could. If they're probes which are flying around for the sake of surveying and prospecting, it wouldn't surprise me if they have long-range sensors for looking for mine-able asteroids and the like.
Someone detects the beast, decides it should be brought in for a closer examination and realises it's not as inanimate as they thought. It could happen.
Especially if they conclude it has signs of engineering or organic life (a visual profile of the Alien could be interpreted as either). We already know anything suspected of ET origin is apparently big enough business to halt and divert an expensive voyage like the Nostromo's. Doubt that's what's happening in
this game, if only because of the differences in the creature design, but I could see it for a movie's set-up.
If people can accept the '
Alien 3' egg, they'd certainly accept this.