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 lacks credibility due to a possible misattribution of historical figures; Simeon Kayyara actually existed in the next era after Yehudai Gaon, leading to discussion about the possibility of a name swap.