Caiaphas did not say this on his own. Instead, as high priest that year, he was prophesying that Jesus would die for the nation,
Textus Receptus (TR) - John 11:51 >Τοῦτο δὲ ἀφ᾿ ἑαυτοῦ οὐκ εἶπεν, ἀλλὰ ἀρχιερεὺς ὢν τοῦ ἐνιαυτοῦ ἐκείνου, προεφήτευσεν ὅτι ἔμελλεν ὁ Ἰησοῦς ἀποθνῄσκειν ὑπὲρ τοῦ ἔθνους,