So Arya replying to Brienne's question of who taught her, "No one," isn't corny, but the cave paintings tying together symbology laid out from the beginning of the series while simultaneously convincing a principle character of the existence of the primary threat of the series, is very corny. Got it.
I don't really care. I actually agree the cave painting thing was lame, but it was also intensely helpful for the advancement of the plot. I don't really care to watch Jon being unnecessarily cryptic about the things he's seen to people he needs to convince to be his allies any more. I just felt like the whole Arya vs. Brienne/two badass female warriors meet/David vs. Goliath thing, and Arya saying "no one" taught her was the epitome of corny. Like the definition of. But it was fan service and I appreciate that.