All of a sudden, he attacked the Mo Clan. After all, he knew that something had happened to Ling Xiaoshuang because of the Mo Clan.
Ling Xiaoshuang had held onto his Heavenly Aqua Saber, which meant that after they had been separated, his Heavenly Aqua Saber had been in Ling Xiaoshuang's possession. Given Ling Xiaoshuang's nature and her relationship with him, Ling Xiaoshuang could not have handed over his Heavenly Aqua Saber to the Mo Family for refinement.
Since she had lost his Heavenly Aqua Saber, which had then been refined by the Mo Family, that meant that they had snatched his Heavenly Aqua Saber from Ling Xiaoshuang.
Since his Heavenly Aqua Saber had been snatched by the Mo Family, it would be strange if Ling Xiaoshuang was well. Thus, he did not ask how or why. He instead directly sneaked an attack. If he had asked how the Mo Family had dealt with Ling Xiaoshuang, he would have lost the chance to launch a sneak attack.