Tried to keep that title spoiler-free for those who haven't seen The Last Jedi yet!
Is Kylo Ren right about Rey's parents
being drunks who sold her?
Based on his motivations I could see him manipulating her, or perhaps... being honest. But how would he know?
This is covered in an interview he did with The Daily Beast.
While he doesn't come right out and say, "yes, her parents were junk-traders", he acknowledges that she is a nobody and comes from nothing.
That was the idea, says Johnson. “That seemed so appealing to me. I mean, that really seemed like something that was genuinely exciting,” he says. “I think that actually gets back to the roots of what makes Luke appealing, because when you’re watching that very first movie, A New Hope, you have nothing in your head about him being the Chosen One or his lineage or this or that. What you see is a kid who’s in the middle of nowhere on a farm, who’s a nobody, who feels like he’s never gonna get out. The same way that when we’re kids on the cusp of adolescence, we feel like we live in a really small world and, oh man, am I ever gonna grow up? Am I ever gonna have these adventures that I keep hearing about on TV?”
“He’s on the cusp of that,” he says, “and then he jumps into an adventure and is pulled into the center of it. That, to me, is the essential appeal of it. And to me, the notion of Rey being a nobody and coming from that and then suddenly finding the power in herself to be central to these big adventures? That’s uniquely Star Wars.”
“I do like the notion, and I think it’s something that’s gonna be necessary, that we’re pulling it away from the idea that [the main Star Wars saga] is limited to this small club of Skywalkers,” he continues. The big reveal had dramatic implications too. “Rey is our protagonist and the truth is, in the story, the toughest possible thing for her to hear is, you know, you’re not gonna get the easy answer that you’re so-and-so’s daughter, this is your place. You’re gonna have to stand on your own two feet and define yourself in this world. And you always wanna throw the hardest thing at your protagonist.”
To be fair, it seems as though each writer/director is being given a fair bit of leeway, and it is possible that the next film by JJ Abrams will retcon this, but for now the word of god is that Kylo Ren was being truthful.
According to the film's director, Kylo Ren certainly believes it to be true (as does Rey), but that's not necessarily the same as it actually being true. Force Visions have a tendency to show the viewer things that aren't true, or are allegorical rather than literal.
“I can’t speak to what they’re going to do. And there’s always, in these movies, a question of ‘a certain point of view,’” Johnson said, invoking Obi-Wan’s line from Return of the Jedi, explaining why he told Luke his father was dead rather than the truth that he had become Darth Vader.
“But for me, in that moment, Kylo believes it’s the truth,” Johnson added. “I don’t think he’s purely playing chess. I think that’s what he saw when they touched fingers and that’s what he believes. And when he tells her that in that moment, she believes it.”
The Last Jedi spoiler talk: Did Rey learn the truth about herself?
and
“In our movie, it’s kind of the opposite,” Johnsons said. “The easiest thing for Rey and the audience to hear is, Oh yeah, you’re so-and-so’s daughter. That would be wish fulfillment and instantly hand her a place in this story on a silver platter.”
“The hardest thing for her is to hear she’s not going to get that easy answer. Not only that, but Kylo is going to use the fact that you don’t get that answer to try and weaken you so you have to lean on him,” Johnson says. “You’re going to have to find the strength to stand on your own two feet and define yourself in this story.”
The Last Jedi spoiler talk: Did Rey learn the truth about herself?
This question needs updating following the Rise of Skywalker, given what we know from that movie we know that Rey
Is the granddaughter of Emperor Palpatine, Kylo Ren only discovers this in the movie.
Therefore in the last Jedi Kylo thought he was telling the truth.
It really is unknown whether Kylo was lying or telling the truth.
In that situation it would make sense to manipulate Rey to get her off guard but on the other side telling her the truth would catch her off guard. `For all you Rey Skywalker supporters I am sorry. It is probably not happening. And for how Kylo Ren would know he might know some people. If she is Luke's daughter then she might have grown up with Kylo so therefore he was lying.
Rey’s parentage was revealed two weeks ago in BATTLEFRONT 2, aint-it-cool
– Peter Turner Dec 18 '17 at 14:02