Whether or not this is a session cookie isn't really relevant. The EU law applies equally to session cookies and persistent cookies.
What you have to decide is whether the cookie is essential for the operation of the site. If it is not, then you fall within the scope of the law and must obtain the visitor's consent. (I know that's an oversimplification, but you were asking for technical advice, not legal.)
Since you are using a third-party platform (Joomla), and since you have no control over what cookies that platform uses (now or in the future), it would be prudent to assume that the site does use non-essential cookies, and to proceed accordingly.