in the American Way magazine, is says that photography onboard is prohibited. (at least it used to a few months ago, last time I checked). For obvious reasons, AA is concerned with pax documenting crew procedures and aircraft interiors (although these could be easily found elsewhere on the internet.). I'm wondering when 9/11 will cease to be the excuse for any arbitrary rule, though.
The FA should have politely informed you of the rule. What you received was typical (in my opinion) of AA's long haul senior FA "customer service".