It's market graded. The coin is actually a 63, but the grader thought it was worth more, so he gave it a two point bump.
Seriously, though, overgrading famous rare coins is not new. Bruce Morelan openly admitted that his 1804 Dollar was over graded, and said that, in his opinion, most of the other examples were, as well.
I will admit that I do not have enough experience with gold coins to know if allowances are made for the difference in hardness of the metal, as compared to copper/nickel, etc. I do recall Mark Feld stating in a post some time back that this may be the case. However, I will say that, if this were a Morgan dollar, for example, I think 65 would be a stretch.