That's a tough one. They were a seated #2 in the west.
They won 13-6 at NY on December 26th, 1969 and then won at Oakland 17-7, on January 4th, 1970.
Apparently the AFL didn't give those teams the name wild card during that post season. I guess we'll just have to say that the Chiefs were the first non-divison champion to win the Super Bowl.