Is Mozilla documentation on checkboxes checked attribute inaccurate?

Checkboxes have a checked attribute. From Mozilla official documentation - it is described as such

A Boolean attribute indicating whether or not this checkbox is checked by default (when the page loads). It does not indicate whether this checkbox is currently checked.

However, many examples and people use it exactly for that reason, to check/dictate whether the checkbox is checked or not. Here is an example

So what is up and down here?