Aryan and Arian are false cognates. Arianism, the non-Trinitarian doctrine in early Christianity, takes its name from Arius, the figure who promulgated it. Aryan comes to us from the Sanskrit, the OED noting:

Sanskrit ārya, in the later language ‘noble, of good family,’ but apparently in earlier use a national name ‘comprising the worshippers of the gods of the Brahmans’ (Max Müller); compare Avestan airya ‘venerable,’ also a national name, and Old Persian (Achaemenian) ariya national name (applied to himself by Darius Hystaspes).

The two words have basically nothing to do with each other, and in fact, although Aryan can be spelled Arian, this spelling is generally not used specifically to avoid confusion between the two terms, which, again, are unrelated. for more on Aryanism, I'd point you here.