No, it is an assumption made by evolutionists, so please don't assert something you cannot prove. If hands and feet can produce extra bones, tissues, skin and so on then so can the coccyx. If "genes for making stuff" were accidently being turned on after 20 million years or so then the entire animal kingdom would be riddled with such cases.
As I said, there are no "genes for making tails". Instead there are plenty of abnormalities that evolutionists can use to pick and choose among in order to provide "evidence of evolution".
Perhaps you think that the Indonesian "tree-man" has "genes for making a tree"?
That would be quite a "throwback"!