The humanoid in question is the following object:
It's basically a straw man used to scare crow. So I think both straw man and scarecrow are valid names for it. However, the dictionary says straw man also has another meaning:
someone, often an imaginary person, who is used to hide an illegal or secret activity
I think this meaning has nothing to do with scaring crow, but I'm wondering, with the existence of this additional meaning, if these two words are still interchangeable when referring to the humanoid without causing ambiguity.