One thing I heard a lot of debate on is how, at least in show canon, only Targaryens can ride dragons, yet Daenerys didn't seem surprised when Jon rode Rehgal.
But I just rewatched the episode, and a couple things came to mind. One, last season, like 7 dudes rode Rehgal all at once during the WW escape. Most likely because Dany commanded / willed it. Told them to get on. She did the same to Jon at the beginning of the ride in 08.01.
However, right before the end of the ride, they very clearly show Jon steering and basically commanding Rehgal to land. Like the beginnings of an actual bond. Dany sees it, and you can see some momentary confusion and surprise. And then they make out and such. But it just made the scene make a lot more sense to me.