I don't think the third-party numbers are high for Alaska; the state has a long history of third parties doing much better than the national average. Also, the current governor was elected as an Independent. Here's a (partial?) list since 1968:
1968: George Wallace got 12.1% in Alaska, a little less than the 13.5% he got nationally but quite high for a non-Southern state (and Alaska is about as non-Southern as you can get!)
1972: John Schmitz of the American Party got 7.2; nationally he got 1.5.
1976: Roger Macbride (Libertarian) got 5.5, nationally 0.2
1980: John Anderson 7.0 (6.6 nationally); Ed Clark (LP) 11.7 (1.1)
1984: David Bergland (LP) 3.1 (0.2)
1988: Ron Paul (LP) 2.7 (0.5)
1992: Ross Perot (Reform) 28.4 (18.9)
1996: Perot 10.9 (8.4), Ralph Nader (Green) 3.1 (0.7)
2000: Nader 10.1 (2.7) Pat Buchanan (Reform) 1.8 (0.4)
2004: Nader 1.6 (0.4)
2008: Nader 1.2 (0.6)
2012: Gary Johnson (LP) 2.5 (1.0)
Not impossible then, although I'd still be surprised personally. I'd say the Johnson 15 is more likely than the Stein 6.