The Generalbundesanwalt (Public Prosecutor General, GBA) is a civil servant bound by his superior's orders. That is why he can always be retired instantly by the Minister of Justice (§54 BBG). So yes, it is extraordinarily stupid for a GBA to against his orders.

In this case, however, I think Range actually wanted to be retired. He has taken so much fire over his apparently incompetent statements relating to NSA spying (among others he confused NSA and NASA on multiple occasions) that he probably wanted to get out of what is otherwise a fairly quiet job. In particular since there is pretty much nothing to gain anymore in this case.