Probably not. The mouse's fur can be messed up in any way. The ancestors of the Thunder Clan will not drag them into a battle that will kill the cat. Goosefeather and Featherwhisker are witch doctors who can interpret signs, and Featherwhisker is Goosefeather's apprentice. Presumably Featherwhisker will not believe that he can surpass Goosefeather, so he follows the clan cats and believes in Goosefeather's explanation.