Hitler did not choose anything in regards to this discussion. Short and Sweet: Aryan was an already designated and ( for those who bought it) proven designation of a superior race that settled in more or less what was modern-day Germany and Scandanvia. All the language and pseudo-science of National Socialism though was born out of 19th century "research" into the origins of the European races.

To pick a few influencial writers:

Max Müller would be the first author in English (though he was German) to write of an Indo-European language/ethnic group called Aryan. Which was modified by French author Arthur de Gobineau in An Essay on the Inequality of the Human Races that advanced the theory that Aryan was not only a race and but the pinnacle of races. The mythos of the "Warrior Race" of Germans was then blended with Germanic tribes battling against the Romans. Then this was then blended with a christian quality in one of the defining works of (nonsense) racial science from Houston Stewart Chamberlain (A Brit who immigrated to Germany and was quite cozy with Wagner) The Foundations of the Ninteenth Century. This isn't even touching on American, Swedish, etc. authors of the 19th and 20th century who all predated National Socialism.

So basically none of this was up to Hitler. He was using terms and concepts rooted in literate predating his ideology.