The term "authorized" probably translates to something like this:
"Hello ECB? This is Richard Faille, I would like to produce and sell zero euro souvenir notes. Here is a sample; these will be made by Oberthur ..."
(Some time later)
"Those are fine, Mr Faille, we do not have any objections."
What I find odd about that media release is the statement that the "concept of souvenir notes is relatively brand new". Now what, "brand new" (nah) or "relatively new"?

Side note: Here is a video that shows a zero euro "note" in a banknote checking device.
Christian