A blanket statement is a generalization with the intended meaning, “All Xs are Ys.”
A blanket statement might say something like, “all movies starring Jim Carrey are funny.” But it could also be more nuanced and be more specific, for example stating:
“all Hollywood blockbusters staring Robert Downey Jr. are focused on how he comes out of prison to find redemption for his past crimes in the movie “Iron Man”.”
There’s some truth in both examples–Jim Carrey ate peanuts before every take of “Holy Goalie!”, and Robert Downey Jr. has had many roles where he was coming back from jail or prison.