A11y: should hidden elements be focusable?

[NoelDeMartin]

I've been reviewing my app for accessibility, and after running an automatic check with axe DevTools I came across the following issue: ARIA hidden element must not be focusable or contain focusable elements

After digging into the code, I realized it's actually a button added by HeadlessUI when a modal is open, in particular I think this is where it's being added: headlessui-react/src/components/popover/popover.tsx#L490..L510.

Now, looking at the code I realize this is actually a button that should be focused, even though it's hidden. So what gives? Is that accessibility rule wrong? Or is there something else going on here?