Absurd native American Law, I know it's not true, but where did the rumour start?

So, someone said something interesting in class the other day. She had apparently heard that;

“if you ride in a covered horse drawn wagon and cover yourself with a blanket, then it’s legal to shoot Indians”.

Make sure you understand, there was no one who believed this was true. I’m just curious how this rumour ever started. Could there be any law remotely similar, whether in the present or the past?

By the way, I’m talking Canadian law here, but it could have started from a United States’ law for all I know.

Never any law even remotely similar. It sounds like somebody was making up jokes.

Did you know that a duck’s quack doesn’t echo…and nobody knows why!

If you google “legal to shoot indians,” you’ll find several “stupid law” websites that attribute it to North Dakota law (without giving a citation, of course).