I think that a better way to word it is "this monster that somehow learned to walk upright"
I appreciate what you're both trying to say, but you both missed the mark. The monster's form does not resemble human, and he's not capable of doing anything upright. It would be convenient to believe his supporters were fooled because he took on human form, or at least walked upright. There's no easy explanation for anyone being fooled by someone so lacking in a disguise.