this is common practice in general no? People ask for references, or try to contact former bosses, when hiring critical profiles. Obviously nobody will say anything bad, so HR is trained, and giving trainings to the hiring managers, how to "grade" the level of positivity.

There's a difference in saying "Yes I confirm person X worked here, he did a good job on all the tasks that we have asked him to do" vs "Yes, he was amazing at his job, he was proactive and really drove innovation, we are sad to see him leave"

> this is common practice in general no?

The German situation is especially unhinged. See https://de.wikipedia.org/wiki/Arbeitszeugnis (ask Google Translate for help, if necessary).