*I agree with you that modern nation-citizenship concepts did not exist...Although Iran as a state concept existed during the Sassanid times as an official name/territory.  In the Islamic era,  geographical-cultural Iran did exist and actually was officially used in the Ilkhanid domain.  Ahmad Ashraf, "IRANIAN IDENTITY iii. MEDIEVAL ISLAMIC PERIOD" in Encyclopaedia Iranica. "The prominent historians of this period frequently referred to Iran and Irānzamin both as historical notions and as contemporaneous entities"  
 *Anyhow these are all besides the discussion...Tusi was simply a Pesian from the city of Tus in Khorasan in modern Iran. 
 *Khorasan, Azerbaijan etc..were definitly not national states..and a national state with the name Azerbaijan officially is from the 20th century.  However, all this does not matter as Tusi is simply a Persian from Khorasan.  We should note the term Iranian at least before modern states 
 denotes Iranian peoples primarily (half of which live outside of Iran).  All that stuff on the side.