This interview was in 1978.
Empire Strikes Back was 1980.
First Star Wars _was_ a very white movie. I suspect the powers that be saw this interview and grabbed Billy Dee Williams to try to give a little better representation.
From a 1980 interview with Billy Dee Williams :
“The introduction of Lando is a good one,” he says firmly. “I talked to George when Star Wars came out and I was very candid. I said, ‘Look, there’s Darth Vader, the dark, black fear, and there’s Alec Guinness playing the white knight, Ben Obi-Wan Kenobi. Here we go again, perpetuating that same old stuff.’
“And now, by having Lando [who slowly becomes an ally of Leia’s cause and vows to rescue Solo], we’re gonna have to put aside the old point of view. Now, we’re talking about symbols—darkness as averse to clarity. Black, white, red, we’re all included in the human dilemma, and Darth is scarier this time, because now we learn he’s human—he’s not a mechanical monster.”
So, they were aware.