I thought Naders best state was Maine, with 1.45% of the vote. His best county was in Idaho, however.
Indeed, Arkansas was in fact Nader's third best state after Maine (1.45%) and North Dakota (1.32%). His second and third best counties after that one in Idaho were both in Arkansas, though.
The PUMA element has some truth to it. Also, the Green Party is a lot stronger in Arkansas than most other states. (Yes, I know Nader was not the Green candidate in 2008, but his association with the party and overall stature were more significant that McKinney's.)
Arkansas was home to the only elected Green Party official in the country. He was a state legislator, if I recall. He later changed party affiliation to the Democrats. Oddly enough, the only elected Green Party official in the country is a city council member in the town right next to me.