Board Thread:General Discussions/@comment-26938547-20170618005726/@comment-4820209-20170618035936

I'd be willing to bet that's more so an effect caused by the mass amounts of dust in the environment around him being disturbed as he moves.

On the conspiracy side, it could also be the remnants of a script where the female MUTO prevented him from using his atomic breath, and said dust is a discharge.