Buying a one-way to the US

[aputman]

I am currently studying in Japan and in need of a one-way ticket home to Detroit sometime in early August. I am a bit confused by the policy:

You can book and purchase a ticket for a one-way flight from Europe, Central-South America, Asia or the South Pacific to the US if you have already purchased a student ticket from the US

I am not sure what constitutes the purchase of a student ticket from the US. I am a student and I did fly from the US to Japan, but I did not use a service such as StudentUniverse.

Anyone with more information or a similar situation?