What exactly is the direct evidence? Does it have post markings?
Based on it's orbit, it almost certainly came from outside our Solar System.
"[...] revealed no signs of cometary activity after it slingshotted past the Sun on Sept. 9 at a blistering speed of 196,000 miles per hour (87.3 kilometers per second)."
That's greater than the escape velocity of the Solar System. Also: It has no "orbit" (elliptical or circular path around the Sun) - rather, its trajectory is hyperbolic, as ground-based observations indicated.
Regards,