We know that (some) knights practised swimming in white harness, ... and other seemingly unlikely feats. Many of these have been replicated (although acknowledged as ridiculously hard) by modern experimental archaeology.
Well, in this case it involved a one-handed guy with a bronze replica hand, wearing a hardened leather cuirass with metal applique, still wearing sword, and heavy boots. The guy pulling him out of the water is wearing a long leather coat, heavy boots, leather trousers. And not only do they not fall into shallow water, we see him unsuccessfully struggling with his armor trying to get it off as he's continuously sinking deeper and deeper, and then they get out of the water a few hundred meters away from where they fell into it.
I'm sorry to say it, but your example fails to convince me that it is applicable to this scene.
If both had come up without all the heavy garment and boots I would be willing to overlook the long distance from the attack site as a means to have the dialog undisturbed from other people, flailing their arms while on fire and the associated screaming that tends to ruin the quiet moment that the two are having. As it was, they created a cheap cliffhanger at the end of one episode, and an entirely implausible resolution in the next one. And even that I might be forgiving if this wasn't supposed to be
Game of Thrones, where the rule established in about 64 previous episodes was that if your character gets into an unwinnable situation, well, he will lose. You don't want him to lose, be more careful when writing up his confrontation. Like, don't try to backstab a flying dragon with a ballista, which already was over the top silly in The Gamers - and that was a a role-playing fan-film
parody.
"It's Fantasy" is no defense, because of the established dramaturgical principles of the previous six and a half seasons. You don't create a massive hit based on such core tenets in storytelling, and then do a 180° and expect me to accept it at face value. If you don't know the full story (and at this point, only those involved with the production do), and you're watching this for the first time, part of the excitement is that you have a number of worthy characters, and neither the best nor the most relatable characters were, up to this point, guaranteed to make it to the end of the story. I will concede that as the story is drawing to a close, the herd of characters has been thinned so much by now that it's beginning to show who will most likely be among the survivors at the end. Nevertheless, these four incidents were massive spoilers, and unprovoked storytelling mistakes.