Probably the agent had no clue about how Schengen works and while checking Timatic read something about National ID and asked for it. Similar things has happened to me in places that are not used to handle a lot of Europeans (the last one in ICN two weeks ago)
National Germany (DE) (I've chosen Germany at random from the list of EU founders)
Residence China (People's Rep.) (CN)
Embarkation Australia (AU) /Transit Qatar (QA)
Destination Spain (ES)
ALSO CHECK DESTINATION INFORMATION BELOW
Qatar (QA)
TWOV (Transit Without Visa):
Visa required, except for Holders of onward tickets for a max.
transit For details, click here time of 24 hours.
- Holders of a prearranged Stopover Paid by Carrier (STPC) issued to those in transit for min. 8 hours and max. 24 hours are permitted to leave the transit area, if holding passports valid for at least 3 months and subject to approval from immigration.
Qatar (QA)
Yellow fever vaccination not required.
Spain (ES)
Passport required.
- Nationals of Germany are allowed to enter with an expired passport. The passport is accepted when expired for a maximum of 1 year.
- Nationals of Germany traveling without a passport must have a document accepted for entry, valid on arrival.
Passport Exemptions:
- Nationals of Germany with a national ID card.
- Nationals of Germany with an emergency or temporary passport.
- Nationals of Germany with a Travel Permit in Lieu of Passport (Reiseausweis als Passersatz) accompanied by an expired German passport, an expired German national ID card or a valid identification document (eg., driving license).
- Nationals of Germany with a Travel Permit Issued in Lieu of Passport for Entry into the Fed. Rep. of Germany (Reiseausweis als Passersatz zur Einreise in die Bundesrepublik Deutschland).
VISA NOT REQUIRED.
Minors:
- All minors who are nationals of Germany are expected to hold their own travel document.