Is there a difference between Low-e Glass And Argon Gas?
Low-E windows are designed with material inside the glass or layered on it at the time of manufacture.

Argon Gas windows are multiple-pane windows that are air-tight with the gap between the panes filled with argon at assembly.

It is possible to get windows that are both at once. A Google search for Argon Windows brings up several links explaining Low-E windows and how Argon and Low-E are not the same.