That part is subtitled as:Easy enough to check the subtitles?
(Yells)
(Viserion growling)
The theory Jon Snow was distracting the dragon for Arya sounds like BS to me. Viserion was already 100% focused on Jon Snow behind his rock; in fact his popping up to yell at Viserion looks pretty comical really. Seems the dragon also made the same mistake as the giant earlier in the episode, which was taking a moment to gawp at the living rather than ending it quickly.
Personally am really needing to see next weeks episode, as this one has just left too many unanswered questions that might be covered later on. It's bad enough we needed the teaser for next week just to be able to tell if Rhaegal made it or not.