doctorbadwolf
Heretic of The Seventh Circle
It's there as misdirection. For the audience not to immediately know Luke's gambit is an illusion, we have to know he has a way back.
I think the two are far enough apart (beginning and end of the movie) that there is more to it than just this.
Specifically, it reinforces the idea that Luke went there to die, and has no plans to return. Who knows if the ship would even fly after all that time.
Also someone else mentioned how he got there without an astromech droid. I am 99% sure the answer is, the Force.