The artist started with an assumption that the dev team animated the UVs for the distortion and then moved a tiled normal map from the top right to bottom left.
"I don’t think that there is any vertex animation, because, on the one hand, I can’t see any movement when looking at it from the side," noted the artist. "On the other hand, they would have to “lock” the border verts and this seems a bit too complicated to me."
It's a really great take on how you can come up with a smart solution that won't harm performance. Make sure to check out Simon's post here.