Galatea's eyes are green while the person she was based after, Supergirl, has blue eyes.
All shots of the attacking soldiers reveal their belts to hold three grenades each, but the belt The Question drops holds four, then two are seen lying around after their owners are gone.
The victim is always referred to as "Gilbert Hallstrom", but the credits list his character's name as "Gilbert Hale".
How would J'onn know that was the man from Supergirl's dream? Even if she described the man to J'onn, without Supergirl to point it out, at best it would be a guess on J'onn's part.