Short answers, pulled from the story.
The Sanskrit word Arya translates as noble, precious, pure, valuable, rich, or not ordinary depending on context. Translators render this single word to describe spiritual warriors or heroes rather than a social class based on birth.
Only the noble ones called aryas can fully realize all four aspects according to the Mahāvibhasa text. That text specifies volume xxvii page 401c29-402a12 where only noble wisdom understands them completely.
Buddhists classify human beings into two broad categories: puthujjanas known as worldlings and ariyans known as noble ones. Worldlings belong to the multitude whose eyes remain covered with dust of defilements and delusion while noble ones obtain status from inward nobility of character.
Paul Williams states that Aryas are saints who have attained fruits of the path leading toward Nibbana. Bhikkhu Bodhi explains how the word noble designates a particular type of person which his teaching aims to create, and Geshe Tashi Tsering describes how arya beings perceive physical and mental suffering exactly as they truly exist without distortion.
The Mūlasarvāstivādavinaya describes Buddha teaching Four Heavenly Kings of the four directions in their own languages. Guardians of the east and south speak Sanskrit while guardians of the west and north speak Dasyu languages.