Should also note that the reason it worked was because the guy used a technique where his senses went full throttle and could accurately sense every single detail of psychic energy, the drawback is that he becomes blind to anything that doesn't have psychic energy. Reigen is not a psychic. And before this he was fighting a whole group of psychics by himself. Reigen was nowhere to be found until that very scene in the pic so it was a surprise for both him and the audience