Why did Lando Calrissian know Darth Vader was after Luke Skywalker?

Question

When Leia, Chewbacca, and Han confront Lando about them being tortured, Lando says that Vader is not even interested in them. He's after somebody named Skywalker.

Leia: Why are they doing this?

Han: They never even asked me any questions.

Lando enters with guards.

Chewbacca growls.

Leia: Lando.

Chewbacca growls even louder and angrier, directed at Lando.

Han: Get out of here, Lan ...

Lando: Shut up and listen! Now Vader's agreed to turn Leia and Chewy over to me.

Han: Over to you.

Lando: They'll have to stay here, but at least they'll be safe.

Leia: What about Han?

Lando: Vader's giving him to the bounty hunter.

Leia: Vader wants us all de ...

Lando: He doesn't want you at all. He's after somebody called ... uh ... Skywalker.

Han: Luke?

How did Lando know Vader wanted Luke?

Did Vader let that slip? Did Lando get that knowledge from other sources? It's not like anybody else with Vader (e.g. - stormtroopers) know about Vader's quest for Luke.

Is this mentioned in the novelization?

Answer 1

Shortly after leaving the torture chamber, Vader speaks to Boba Fett and mentions "Skywalker" by name. Lando is present.

Vader: You may take Captain Solo to Jabba the Hutt after I have Skywalker

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This conversation goes slightly differently in the original novelisation

Outside the torture chamber, Boba Fett waited for Lord Vader with Lando Calrissian and the administrator’s aide.

With obvious disdain, Vader turned to Fett. “Bounty hunter,” Vader addressed the man in the black-marked silver helmet, “if you are waiting for your reward, you will wait until I have Skywalker.”

The self-assured Boba Fett appeared unruffled by this news. “I am in no hurry, Lord Vader. My concern is that Captain Solo not be damaged. The reward from Jabba the Hutt is double if he’s alive.”

_{^{Star Wars Episode V: The Empire Strikes Back - Official Novelisation}}

This scene is replicated in the new (canon) junior novelisation, but again the dialogue is slightly different.

Lando is waiting outside the door when Vader leaves the room. “You said you wouldn’t hurt him!”

Vader sweeps by the old cardsharp to where Boba Fett, the bounty hunter, is waiting.

“Once I have Skywalker,” Vader intones, his voice a gentle tapping on the galaxy’s largest, deepest gong, “you may take him to Jabba the Hutt.”

_{^{The Empire Strikes Back: So You Want to Be a Jedi?}}