> The standard date format is YYYY-MM-DD (it's also the date part of the ISO time format)

Strictly, it is the extended form of the ISO 8601 calendar date format. (The basic format has no separators.)

ISO 8601 allows any of its date formats (calendar date, week date, or ordinal date) to be combined with a time representation for a combined date/time representation, it is inaccurate both to call any of the date formats part of the time format, and to call the calendar date format the format that is part of the combined date/time format.

(There's a reason why people who want to refer to a simple and consistent standard tend to choose RFC-3339 over ISO 8601.)