Route is flown by an A320. DL is in the process of putting AVOD in all the A320's, but has not quite finished yet. 37 out of 62 aircraft have been modded to the A32M configuration with AVOD and another 3 are currently in mod's and there are 22 A32K's currently flying without AVOD.
The Official Delta A319/A320/A321 Cabin Mods Thread
True. I didn't even think about the possibility that it could have been an older A320 that wasn't refurbished / updated yet, If that's the case, those amenities wouldn't have been listed online when the ticket was purchased, and there wouldn't be any reason for the flight attendant to make an announcement about it.