Comment by endorphone

Professional pursuits are things related to a vocation, not directly tied to an exchange of money for every interaction under consideration. If you're in the industry of software development, and tie your identity to an open source project, it is de facto professional.

In this example it is held as a significant accomplishment on this individual's linkedin page. Which isn't surprising as professional credibility is a primary motivation driving a lot of open source involvement. We are seeking a different, less direct form of compensation.

So it's fair to say that acting like this is unprofessional.

That doesn't mean it isn't merited, or that they might have been frustrated or had good reason. But professionally they would have been much better served by other means: Simply announcing that they're retiring from the project and encouraging forking and the percolation of a new canonical version, etc.