@Gran Guitarra

I believe that Arrian and other historians who recorded Alexander's campaigns were very loose with their terminology. The argyraspidai were created in India by Alexander, but every now and then they were still referred to as 'hypaspistai'. Not to mention things like the so-called 'Seleukid legionnaires' still being referred to as argyraspidai. In fact, records of the Seleukid-Roman Thermopylae refer to the Argyraspidai as peltastai! So it would not be wise to take the naming literally.

Especially when the Asthetairoi refer clearly in the Alexandrian case to a phalanx soldier who was a townsman or citizen, it could just as easily be just a synonym for the Pezhetairoi, who were Makedonian citizens. After all, one is 'Foot Companions' and one 'Citizen Companions', they are not necessarily mutually exclusive. It would be the equivalent of Homer using different adjectives to describe Iliad heroes. 'Well-greaved Achilles' and 'Stout-speared Achilles' do not indicate different people named Achilles.

For some idea of just how confusing the Greek historians made naming conventions, refer to 'The Seleucid Army: Organisation and Tactics in the Great Campaigns' by Bezalel Bar-Kochva. There's a whole chapter on the nature of recruitment of Klerouchoi and Argyraspidai that should utterly confuse you by the time he finishes discussing the different contexts and usages of the words. As said before, Agema, Hypaspistai, Peltastai, Chrysaspides, Chalkaspides and Hetairoi all enter into the chapter at some point or other.