In the books, Hardhome happens "offscreen", with only rumours and reports coming back to the Wall of what happened there. This plays into the strengths of the written medium, and especially so since we're learning of the events from an introvert and thinker like Jon. The books have the benefit of using mounting paranoia and fear of the unknown, because we have a direct link go the character's thoughts.
In the show, we don't have that luxury. What they did was twofold. Firstly, they focussed in on some of Jon's other qualities - his desire to do the right thing, and his leadership. Secondly, they used the strengths of the visual medium to translate something which had been communicated in a very "booky" language.
In short, they translated something which had relied on the facets of the written medium into something that effectively used the facets of the visual medium. It's quite literally an adaptation.
I think this is a fair viewpoint on a thematic level, and it's certainly somewhat true, but as far as the specific subject matter goes though, I disagree. Hardhome is not a cinematic adaptation of something that was alluded to in the books because it's either a completely different situation and context, or it simply hasn't happened yet.
In the books, the stories told of Hardhome are not about some huge battle between Wildlings and White Walkers, but rather about survival in the harsh wastes, clinging to hope of a prophecy, and people descending into madness. Cannibalism, looting, slavery, etc. It's about opportunists taking advantage of a broken people, and how Jon's goodwill mission found only the heart of darkness instead. It's not even remotely the same. It isn't something that just happened "off screen", it's something completely different.
Now it's possible that Tormund's mission to Hardhome in the books might be closer to what happened on the show, but that hasn't happened yet, so we have no idea!
