Technically, Hayek is not an Austrian in the “Rothbard Mises” strand of Austrian economics. He did favor empiricism, mathematical equations, and indifference analysis, ideas that go directly againist major “typical” Austrian tenets. From Bryan Caplan’s “Why I am not an Austrian Economist”
“Contrast Mises and Rothbard’s stringent rejection of mathematical economics with Hayek’s desire to “…avoid giving the impression that I generally reject the mathematical method in economics. I regard it as indeed the great advantage of the mathematical technique that it allows us to describe, by algebraic equations, the general character of a pattern even where we are ignorant of the numerical values determining its particular manifestation. Without this algebraic technique we could scarcely have achieved that comprehensive picture of the mutual interdependencies of the different events in the market.” (F.A. Hayek, “The Pretense of Knowledge,” in F.A. Hayek, Unemployment and Monetary Policy (Washington, D.C.: Cato Institute, 1979), p.28.”
As Caplan correctly noted in his earlier paper regarding Austrian economics, if Mises and Rothbard are correct, neoclassical economics is all wrong; if Hayek is correct, neoclassical economics just needs to adjust its focus.
As for why he is considered an Austrian economist, it probably has to do with the fact that 1)he made important contributions to Austrian capital/ABCT theory (among other areas listed by Esuric) 2)Less stringent Austrians would still consider him a bread and butter Austrian 3)He is easily the most famous Austrian economist, aside from Schumpeter (and he is pushing it to be considered under the “Austrian” aegis).