Even if it was indeed a shot of them leaving Sunspear, the distance from Meereen to Sunspear is incredibly vast. So whether Varys went back and forth or Dany's fleet just joined them in Dorne, it's ridiculous time compression either way.
I think it was a poor decision to end the season with her sailing for Westeros/KL so soon, but maybe that indicates there's so much crap to still happen over the next two seasons that the time compression was necessary. After all, there was a mega time crunch to get the Greyjoys to Meereen so bloody fast earlier in the season, and we've yet to see where in that journey Euron is. (Perhaps we're due for a scene with he and his men on a 'side quest' raiding and plundering somewhere. I dunno anything about him, having not read the books.)