Scorpius is equally surprised by the love and trust implicit in the offer, though it doesn't come quite as suddenly to him after their intimate conversation in the cave. Harry ends up doing exactly what he advised him to do. Acknowledge the runes, overlook the creepiness - and it's far more than an apology. It's an appreciation of Albus" dark side, a way to channel it into something more positive. Ever since their conversation in the cave, he's been wondering how Harry would approach his son, and suddenly he comes up with something so specific, yet so unconventional, that it suits both of them.