Very interesting point. From the website (bolding is mine). Note the part about canceling via website or app.. implies that canceling via agent does not qualify.

AAdvantageŽ members may be able to cancel Basic Economy fare tickets and receive travel credit for a fee. To qualify: 

• Your AAdvantageŽ number must be in your reservation before canceling
• Your trip must be booked in the U.S. directly through American
• Your trip must be on an American marketed and operated flight starting in the 50 U.S. states
• Cancel on aa.com or the American app before the first flight departs

If the fee is more than the ticket price, travel credit will not be issued.