That has changed now. Back then you could choose credit cards as the form of identification for online tickets, nowadays however they don't assign a specific form of identification, but rather require passport, ID card or similar:
- Passport
- European government-issued ID card
- Child's passport
- BahnCard (in accordance with the Conditions of Carriage, a BahnCard is only valid in connection with a photo ID, which may have to be presented on occasion)
- Electronic residency permit
- Certificate for asylum applicants
Please note: driver's licences are not accepted as a form of identification for ticket inspection.
from
https://www.bahn.com/en/view/booking...e-ticket.shtml