There are various categories where the states or federal have the power to enact laws. In this case, it is part of the competing law section: As long as the federal government has not provided a conclusive law on the topic, the states may make their own laws. For renting there is conclusive law, so states are not allowed to make new laws regarding the topic.
Yes. That's probably the analogous name from the english language sphere. In German, the rule is named "Bundesrecht bricht Landesrecht". I made a more direct translation to make it more similar to the original German name. https://de.wikipedia.org/wiki/Bundesrecht_bricht_Landesrecht
The phrase "Bundesrecht bricht Landesrecht" is even part of the German constitution, as Article 31.
Shorter press release (German, too): https://www.bundesverfassungsgericht.de/SharedDocs/Pressemit...
It's a classical application of the "federal law breaks state law" rule, which I think exists in the united states as well.