I'm a bit surprised. I thought the referendum over this wasn't due for another week, since there will be general and state elections next sunday.

This looks like a hail mary move before elections could have switched up majorities and brought a change in administration. As a born-Berliner I'm highly critical of this populist move, that was mainly organized by transplants who demand stuff for free all the time: UBI AND open borders. Unfazed by the fact that somebody will have to foot the bill for socialist cloud castles eventually. These people will move back to their hometowns when they have made the living situation in Berlin become untenable, for me it's my home and where all of my family lives.