I thought so too.
How did Flash get to Supergirl's Earth again? It seemed funny to me that he needed her to get back but didn't need her to get there.
He got there by accident. Apparently just from moving too fast? Which is weird, since previously moving too fast wound up accidentally sending him through time, not dimensions. I suppose it might have had something to do with that thing on his chest.
But that was a major hole in the episode, especially since their solution was again just moving really fast, yet he somehow needed her help to move fast enough. Is he slower on her world or something? If he could accidentally get himself there, his speed should've been enough to get himself back.