It seems like Grand Priest trained goku omen ultra instinct to attain Ultra Instinct Omen. It’s not confirmed yet but I think it’s very possible. Goku was able to achieve it twice on his own and now it wouldn’t be so surprising that with some special training with the Grand Priest helped him achieve this form. It is also more practical to attain full control over this form before he even tries to attain the mastered Ultra Instinct form. Still, he looks so good in this scene!