This statement cannot be relied upon, as Simeon Kayyara in fact lived in the century following Yehudai Gaon; and Halevy is of the opinion that the names were inadvertently switched, though this reading creates as many problems as it solves. The Ramban in his preface to
This assertion cannot be trusted because of an apparent mistake in identification; Simeon Kayyara actually resided in the following century after Yehudai Gaon, prompting consideration of a possible mix-up of names.