Thanos only killed HALF of the Asgardians when he took the Tesseract & blew up the ship. That's what Thor told the Guardians when they picked him up.How exactly is there a 'new Asgard'? Didn't all the Asgardians get on the ship at the end of Ragnarok? Didn't that ship get blown up at the beginning of Infinity War? Where did all these people come from and how did they get to Earth?
It's not been revealed if Thanos LET them escape or if Valkyrie & Korg left before the attack in escape pods while the others stayed back to fight.