That's a bizarre comment because the least protected thing here is the idea. This guy is free to get a new job and write a new library from scratch, or just tell his new company to do X + Y.
Also, of course, German law does not allow the US-style overarching IP clauses at all.
> This guy is free to get a new job and write a new library from scratch, or just tell his new company to do X + Y.
But that’s not what’s the issue at stake here. If I understand the tweet correctly, the code in question was written during the time of employment, though in their spare time. Depending on the exact situation, this could be problematic - for example if internal knowledge of the employer was used or if a profit motive enters the picture (sponsorship for the open source library, as in this case) Both would no longer be an issue if the code was written after employment ends, unless there’s an explicit noncompete in place.
Also, of course, German law does not allow the US-style overarching IP clauses at all.