"Looking for an unambiguous calendar-and-clock format that is internationally understood? It’s time for ISO 8601."
"ISO 8601 tackles this uncertainty by setting out an internationally agreed way to represent dates:
YYYY-MM-DD
For example, September 27, 2012 is represented as 2012-09-27."
The comment you've replied to is a counterexample to this claim.
For example, the meaning of the word "ambiguous" is not ambiguous. If somebody were to ask what the word meant because they did not know the definition, it wouldn't make the word's meaning ambiguous. It would make that person uninformed.