re: Crackpot ASOIAF Theories SPOILERS

I think he may be referring to how Lyanna and Brandon were both excellent horse riders, and people used to say Lyanna was 'half a horse' herself (some think that she may have been warging her horse on some level). Therefore Jon has a natural riding ability like his mom and uncle, due to the Starks being wargs/skinchangers, which was latent until the beginning of the series.

From the AWOIAF:

quote:

---

Lyanna rode horses like a northman. Harwin compares her riding skills to those of Arya Stark.[4] Barbrey Dustin reports that both Brandon and Lyanna loved to ride. She compares them to a "pair of centaurs".[5] Roose Bolton claims that Lyanna was "half a horse herself", probably meaning a centaur, however, he also claims that his son, Domeric Bolton, could out-race her.[6]

---