Did Kenobi go looking for Vader?
How orchestrated is this meeting?
Looks like Vader went walking around the corridors next to the hanger bay, seeking Kenobi.
Maybe he could psychically 'feel' Kenobi's presence.
Or maybe he knows Kenobi's tactics well enough that he could surmise he'd try to sneak back to the ship.
Or, far more likely, perhaps he just scanned recent security tapes.
Jedi mind tricks might work on people, but they don't effect recorded media.
Actually it may not even be that complicated.
Maybe they just called each other.
This encounter finds both of these old duffers nervous, evidenced by their respective goofy taunts:
These two have been waiting for two decades or better to try and kill each other again.
Now that's hatred.
Two of the fiercest warriors of a bygone war, their bodies are now weak and shattered.
Vader does not seem to be using his cyborg tech to assist him much.
As a point of honor he may be using just his own strength.
Compare his performance here with the later duels with his son, where he pulls out all the stops.
Again, this may all just be evidence that this is not a real fight at all, merely a carefully staged distraction.
Vader needs to ensure that the Princess escapes and Kenobi needs to ensure that Luke wants to kill Vader.
Apparently Kenobi lights his lightsaber after Vader, who seemingly appears on the scene with his already lit and ready.
However, Kenobi IS the first to strike.
In Empire, 'Yoda' emphasises a self-defence-only approach to Lightsider Force practition.
Luke will later ALWAYS light his saber first and strike first
(at one point he will even attempt to strike at an unarmed old man with a lightsaber. The kid fights dirty).
Painfully slow, they circle each other swiping away like a pair of... well, like a pair of old men with swords.
Vader realizes that Kenobi is going to lose:
The line, "You should not have come back" sounds a bit wistful or regretful.
We never get to know how this affects Anakin as the movies make every effort to only show us Anakin's business end.
When Kenobi spots Luke he gets an incredibly smug look on his face.
He has implanted Luke with hypnotic suggestions and obviously he feels this will cement the deal.
He wants Luke to see Vader strike him down.
This should imprint in Luke the idea of Vader being his enemy, and make Luke seek revenge for Kenobi's death.
In the process, Luke is now set to believe he will be a Jedi knight.
Luke never gets the training necessary to become a Jedi, but the power of suggestion is strong in this one.
Kenobi wants Vader dead.
He has told Luke that Vader killed his father and now through hypnotism and trauma he has constructed a delusional madman.
Luke very quickly comes to believe that he has special powers of a magickal nature.
Because he believes this, he is able to perform feats of superhuman intensity and ferocity
Kenobi has tried his best to create the ultimate hitman and unleash him on the Empire and on Vader specifically.
He did a good job.
Kenobi, that groveling dog of the Jedi, has doomed the galaxy to slavery under the tyrannical rule of a halluciniatory psychopath.