I read on a Facebook post that:
1. While Jon and the dead dragon were facing off, that Jon saw Arya making her way to save Bran, so Jon confronted the dragon and yelled "Go, go, go!!!!" to Arya to draw it's attention from her.
2. Then Arya whisked passed the WW and you see him notice something and his hair moved.
3. Then Arya killed the NK.
I didn't catch what Jon was doing in 1 above, while I watched the episode.