Wow, this really is great. I'm jealous of how it's all put together so well, so you can't really be any more sure than Horace is whether he's just hoping-and-remembering, or is right (I mean, I know it's a Snape exchange, but I would have bought it as Snape fic even if he'd been wrong and the Snape part was the hope and remembering. But I'm glad he was right).
As others have said, coffee girl=WIN. Highlight of my day, yes.