We should take his story as an example or a to-do list for when we find ourselves trapped in a situation like this- when somebody else takes credit for something we did, especially in the workplace or university, for example.
This never happened to me at work, but it happened to me repeatedly in school. People get really weird when they have to work as a team. In teams, we discover very valuable things about other people's characters and egos. Some people work without saying anything and add value to the team without getting their egos enmeshed in everything.
To me, the worst kind of partner to work with is someone who'll think every good idea is their own, even if they weren't even present when it came up, and those who won't accept criticism, even in the slightest. Sadly, the world is full of those people, and part of the work is learning how to elude conflict with them and, hopefully, integrate them in a way that doesn't trigger their wounded egos.
This employee already had a conflict with a personality like this, and managed to de-escalate it. So we should take a really close look at what he did. Part of the reason he succeeded was that he stopped defending himself emotionally, as commentators on his previous post told him, and limited himself to bringing concrete receipts of his work.
Luckily, this is a real blemish on the thief's employment history, and will likely evoke further management evaluation. At the same time, the other employee showed he can create and fix a project for a higher position. A win is a win!