Does Multiattack for a monster mean it can attack multiple PCs?

@mikemearls Does Multiattack for a monster mean it can attack multiple PCs or just attack with its attacks against one target?

— Andrew Noffke (@GrandMoffNoff) June 28, 2016

It can attack multiple targets, unless it says otherwise. https://t.co/oyNkzbsKN5

— (((Mike Mearls))) (@mikemearls) June 28, 2016