Just as calling the maintainer's offer extortion is not correct, I think it's also to call the email a threat is not correct. It's at worst entitled and slightly aggressive in the part that we saw.
It's pretty shocking that someone in the industry so long thinks that OSS maintainers owe him anything though, or that he didn't think to simply fork his own version - he must know this is an option. He's probably read the MIT license at some point in his career - has he never stopped to think about what to provide something 'as-is' means? His position suggests that he has the resources available to do a lot of things that were far less embarrassing than asking someone who owes him nothing to make his job easier.
It's pretty shocking that someone in the industry so long thinks that OSS maintainers owe him anything though, or that he didn't think to simply fork his own version - he must know this is an option. He's probably read the MIT license at some point in his career - has he never stopped to think about what to provide something 'as-is' means? His position suggests that he has the resources available to do a lot of things that were far less embarrassing than asking someone who owes him nothing to make his job easier.