Had the same issue. Its like FAB use 20 years old censoring algorithms that detect orange/skin color and tag it as mature.
I published model of a gun that had orange wood furniture on it and it was market as adult content. I applied for checking it again by “human”(bet it was just another automatic system) and it was still market as mature.
What I did was… change colors of preview images to be more grey and it passed without any issues…