Board Thread:Episode Discussions/@comment-1181222-20170405101958/@comment-734582-20170411101358

Kjubi wrote: This pic? I think so Kishimoto himself confirmed a third otsutsuki was planned for the movie but scrapped (Probably to streamline the story). Since the Anime did include him, i think it's clear that this was no mistake. Considering Boruto's curse mark origin and the similarity to kawaki's, i think it's pretty much confirmed the Third otsutsuki exists and gave his mark to Kawaki.

I've posted this theory before.