Firstly, imposing on someone else’s intellectual property is not “illegal”, because that usually refers to crimes. This is a civil issue, as in the some company is demanding the dev stops or else they’ll sue him or something.
Secondly, it doesn’t really matter whether the dev is “right” or could prevail against a legal claim - because you just wouldn’t bother trying. Imagine you have an ok job, take care of your family, and made this plugin on a whim just because you can. Your days are full of taking your kids to the park, spending time with your wife, playing around with your hobbies, that stuff. Maybe you’re not wealthy, but your salary is enough to look after your family and make your mortgage repayments. Then Haier threatens to sue you, and although you could likely prevail mounting a defense would probably cost you a years worth of mortgage repayments. Maybe you could represent yourself but that might take a years worth of saturdays writing and responding to legal stuff that you don’t really know much about. Bear in mind that there’s no financial support from the open source community.
It just doesn’t really matter whether Haier has a legit claim.