Never noticed this language on the AA site before, but I assume this has to do with the relatively new DOT refund rules.

Looks like if your flight number changes (even if the times didn't), then you would qualify for a refund if you decide to cancel?

Source: https://www.aa.com/i18n/customer-ser...rvice-faqs.jsp

Their SalesLink guidance on schedule changes also has similar language:

"Refund to original form of payment is allowed in the following scenarios:

· Schedule change results in a flight number change – Schedule change resulted in a flight number change even if flight times on origin or destination did not change"