The assembly seats in Brussels, so the decision comes from Brussels (geographically).

It doesn't imply that people from Brussels are the ones to decide, not everyone has the same idea anyways. Though, as citizens of a EU member state, they have some responsibility, at least indirectly.

>The assembly seats in Brussels, so the decision comes from Brussels (geographically).

Except that half the time the assembly seats in Strasbourg. https://en.wikipedia.org/wiki/Seat_of_the_European_Parliamen...

Brussels is the seat of five governments: the city itself, the Brussels-Capital autonomous region, the Flemish Parliament and Government (luckily the Wallon Government seat is in Namur), the Belgian Federal Parliament, and the European Commission and Parliament.

The "Brussels" metonym is probably the most ambiguous reference to a government body on the planet.