It sounds as if you have Business Platinum? When you use Membership Rewards points to buy an airline ticket you are making the purchase through Amex Travel (Expedia). The last ticket that I purchased recorded the transaction as "PwP AMERICAN EXPRSEATTLE WA" with "DELTA AIRLINES" on a separate line. This is different from the way a direct Delta purchase would be recorded. I cannot say if it would trigger a Delta offer.