There is another interpretation of the legend that Makibi was kept to stay in Tang for a long period of time because he was so smart that Genso (the sixth Emperor of Tang) did not want him to leave Tang.
真備が長期間にわたって唐に留まることになったのは、玄宗(唐)がその才を惜しんで帰国させなかったためともいわれる。