80m dipole bouncing signals to Washington (13135.1 km) on 17m!

Just checked the performance of my 80m dipole on 17m as it had tunable SWR on that band with the auto-tuner on my FT-710 radio. I was really surprised to see my signals being picked up at N7DED, a distance of 13135.1 km, all the way up to Washington, on the Western side of United States. Usually I see pick up of my signals to the maximum on the Eastern side of US, which is nearer to my location. That was considering short path. But for long path propagation, which is more likely, at this time which corresponds to greyline propagation, the distance is 26868.1 km! Why did 80m dipole work so well on 17m? When I checked, the ratio of frequencies, 17m band comes as roughly the fifth harmonic of 80m band. We know that center fed dipole antennas perform well on odd harmonics of the fundamental frequency, a wonder of harmonics in amateur radio, as I had posted earlier. Incidentally, this antenna has tunable SWR on 6m as well, may be around 13th harmonic!