Whom can one not elect directly as a citizen in Germany?

EDITORIAL LEARNING AID

Why is this answer correct?

The Federal President is elected by the Federal Convention, not directly by the people (Article 54 of the Basic Law). Members of the European Parliament, the Bundestag and the state parliaments, by contrast, are elected directly.

The Federal President is elected by the Federal Convention.

This translation and explanation are editorial learning aids. The official German wording and answer key govern the examination.