alt Hacker NewsIt sounds like the maintainer you're describing was underhandedly helping their users with the silent expectation that they also contribute back to the project and got bitter when it didn't happen that way.
Open source is altruistic, remember. You explicitly tell the world that you are happy for anyone to only take from the code what they want for their own needs and never contribute back. If you don't want to help users or develop your software alone, an alternative is to sell the software and support service to users and use the money to hire developers.
I think I know the pattern they are describing, and it's a semi-unfortunate one.
People make a fairly-complex open source thing. Due to the complexity for certain environments/cases, the author(s) have a commercial support option.
Consumers from bigorg use it, and wind up opening issues wanting free help for their niche use case, no they don't want to get a support contract, but this subset of the user base causes a lot of churn dealing with communication, politely closing such issues (after all, you want to just be polite about support options, not drive them away!)...
And sometimes, it becomes easier to just flip the license.
In the .NET ecosystem, it's come up frequently. There's the cases where I get it; PDF is hell (iTextSharp), Imaging is hell (ImageSharp), Auth is hell (IdentityServer).
But then there's the cases where I just shrug my shoulders (MediatR has plenty of alternatives) or get happy it gives me permission to gleefully get rid of a poorly used lib (AutoMapper).