In their examples, none of their buttons were actually buttons. Nor were they even links. They were all DIVs. This is pretty terrible HTML, for many reasons, especially for accessibility.
There are tags you can put on your markup that will tell screenreaders and other accessibility tools that this thing is a button, there is an entire set of aria roles and states for things like checkboxes, buttons and other ui objects so you aren't limited to the defaults provided by the various html standards.