Now that Microsoft is offering a packaging of Linux inside Windows (Linux subsystem), by continuing to charge for their old file systems use on phones with Linux, it was basically saying they can access all of Linux for free but to use a small old part of their operating system costs money. In other words it was very unfair. And possibly asking for legal action.
Now it's slightly less unfair although it's still questionable that Windows isn't providing _any_ monetary support for Linux that they embed.
How? Linux is intentionally released under an open source license. As far as I know, MS follows that license to the letter. How is that unfair? Things don't have to be perfectly symmetric to be fair.
I do think using the FAT patent was wrong on its own, because it was about interoperability when using the one filesystem that can be used everywhere. But I don't think fairness has anything to do with that.
Now it's slightly less unfair although it's still questionable that Windows isn't providing _any_ monetary support for Linux that they embed.