Bending the high notes is a very different technique from overblowing, which involves the 1, 4, 5, and 6 holes. The high notes bend naturally and relatively easily to the next note down, whereas with overblowing, the blow note jumps to the next note on the scale from the draw note. It's an odd and tricky technique. I have heard arguments that some earlier harmonica players were able to do it, but this should not be confused with what Jimmy Reed, or more extensively, Rhythm Willie did with the high notes in 1st position.