If I had to guess it went something like the OP's wife wanted a tool like this, the OP built the tool and made it to her needs but also public so that others could also have the same benefit. He's a HN user hence the Show HN and since it was an itch he scratched for his wife he put that in the title.
Not that complicated really. It could have been more clear with something like "A meal planner I made for my wife", but hey.
Show HN is not limited to startups out of Silicon Valley. It's literally just a prefix to say "Hey HN, I want to show you something I built..." In this case, you can add "for my wife..."
Of course, judging by some of the comments, he'd have to add: "because she wanted this thing, and I figured it others might find it interesting" for those that like to infer things that were never said.
Hackers build things to scratch itches, and then they share them. The fact that it's a particular other person's itch that got the ball rolling is interesting and potentially inspirational.
