In Avengers: Infinity War, when Thor first talks to the Guardians, he told them that Thanos killed half the people on his ship. Untrue. He killed everyone except Thor. Nobody was moving except for Thor and Loki, and then Loki got killed. Thanos then blew up the ship. Nobody was alive on that ship except Thor. Only Thor got picked up. Um, what? What motivation is there to lie?
He doesn't lie
We see that in this very related question: What is the fate of the Asgardians at the start of Avengers: Infinity War?
According to the Redditor, Russo confirmed Valkyrie did survive Thanos’ ambush. The director did not say how, but he did say a portion of the Asgardians also survived. Russo said escape pods ferried those survivors away from the battle, giving the Asgardian race the chance to escape extinction. It is very possible the Valkyrie was charged with overseeing that evacuation since most of the Asgardian refugees were simple civilians.
As some Asgardians beside Thor survived we can see that Thor does not lie.