Your first one is creating a UTC date but you're displaying it in your local timezone. From the documentation...
Support for ISO 8601 formats differs in that date-only strings (e.g. "1970-01-01") are treated as UTC, not local
Your second date is being created in your local timezone. The reason for this is because the ISO 8601 standard only supports a 4-digit year (by default), therefore it does not qualify for the above condition.
