The absence of an ETOPS sign wouldn't be conclusive - you cannot prove a negative (unless a check for such indication was part of a checklist).
I realize that corny folk sayings don't have to be logical. But 'you cannot prove a negative' is itself a negative statement, as in 'cannot', and if it were true, it would be unprovable, right?
ETOPS may be new on the AA A321 fleet but American has operated earlier ETOPS planes like B-767's and A306's for well over two decades I would say.
On the other hand, domestic and international (including overwater to HNL) operations are often like having two separate airlines within the same carrier.
A lot of the domestic folks never venture out over the water. And international folks like me are terrified when they takeoff and land without having to clear customs.
So, the A321 crews may have had something like a day of fire hose ground school, a sim session and a line check as their total ETOPS training and experience.
And, American just completed merging operations with US Air so the paperwork may have been new even if the pilots had, say, flown the ETOPS B-762's or A330's out of CLT or PHL.
A lot of chances for an operational mistake, glad to hear the captain didn't get hanged for this one.