Dear @Ioppo,
Welcome to the Wefugees Community and thank you for your question.
You are right - this is strange as the section 28 (1) no 1 of the German Residence Act (AufenthG) is indeed exclusively for the spouse of a German citizen. You came as an employee of a company with a branch in Germany, right?
I would recommend to contact the immigration office for clarification.
In any case, please don't hesitate to get back to us with any further questions or to keep us updated on this.
All the best,
Meike