First of all Ernesto Guevara was a fighter for freedom and a great revolutionist. He became a symbol of all countries of Latin America, fighting for their independence from foreign capital. Che believed , that the major mean of changing society was revolution. And he was right, that was prooved on Cuban example.
When the freedom was gained, revolutionists began to build socialist state. That was first socialist state in all Latin America. Cuba had closest contacts with the friendly USSR. Che started thinking about making new society, with new men, who would have another thinking , different from capitalistic traditions.
Ernesto Guevara was revolutionary communist, his favourite teachers were Karl Marx and Lenin. His way toward communist ideology was slow, but progressive. The ideas of great communists helped him in his fight against American imperialism in Latin America.
Besides this, Che was romantic. Guevara saw his life as a constant revolution. He wanted to free all Latin America from regressive regimes of capitalism. Che believed in export of the revolution.

I am sure that Ernesto Che Guevara wasn't anarchist. But many anarchists made Che their hero. I watch those demonstrations on TV and see red flags with Che on them. Anarchists think that Guevara was one of the fathers of anarchist ideas, but they are mistaken.
Why shouldn't anarchists put the image of Bakunin or Kropotkin on their revolutionary flag???