There's a difference between information leaks and someone in a position to know breaking Rockstar's request for silence.
Of course, it's conceivable that Rockstar knew and approved of Flying Lotus' comments in advance, since his set list when he made the annoucement was apparently made up of mostly new material. Rockstar may well have let him break silence so that both they and Flying Lotus could reap the rewards of it: they get extra publicity because Flying Lotus debuted new content, whilst Flying Lotus gets extra publicity because of the GTA annoucement. And it's only a minor detail; it's not like Flying Lotus let slip that there will be a fourth palyable character or whatever.
Still, I can't imagine that they would be happy about this.