OneWorld Emerald traveler (AA Exec Plat) on an AA booked Qatar codeshare on Qatar metal, DFW-DOH in paid business. Connecting flight in Doha from DOH-BOM on Qatar codeshare with IndiGo airlines (ticket labeled "Qatar Airways"). The IndiGo segment was in economy as this flight didn't offer a business class option. Was denied entry at the Al Mourjan Business Lounge and told the arriving flight doesn't count, only the outgoing connecting flight. I don't believe this is correct. Am I wrong here, or should I have been allowed entrance?