Question: Key Operation of Dropdown menu

Hi,

I would like to ask a question about implementation of dropdown menu created with WAI-ARIA.

https://wet-boew.github.io/v4.0-ci/demos/menu/menu-en.html
In this example, there are three types of dropdown menus at the top left corner. The labels are “Section 1”, “Section 2”, and “Section 3”. A breadcrumbs menu is placed just below of the dropdown menu.
When tabbing this example page, the focus is on the menu of “Section 1” first, and next, it moves to “Home” in the breadcrumbs rather than to “Section 2” which is next to “Section 1”.
To move to “Section 2” from “Section 1”, the right arrow key must be used, which means users can operate the dropdown menu with keyboard as long as following a specific key operation.

I’m wondering if this example is surely sufficient to WCAG 2.0. I think it might have to provide an instruction of how to operate the dropdown beforehand.

My question is:
Is this key operation sufficient to WCAG 2.0? (the point is this implementation does not depend on tab key operation)
In this case, is it necessary to describe how to operate the dropdown menu with keyboard in order to meet SC of WCAG 2.0?

I would highly appreciate, if someone kindly would give some good advice to me. Thanks in advance.


Many thanks and kind regards,
Satoko