Differences in Human-Machine Interface
The consensus on this thread is that on while on Autothrottle on:
B The TLs move to match the commanded thrust such that on A/T disconnect there is no change in thrust.
AB The TLs do not move to match the commanded thrust such that on A/T disconnect, the thrust changes to match the TL position.
The AB logic is reasonable on its face as long as the crew remembers to move all TLs to idle on the flare -- but fails on human-machine interface criteria because it can put the crew in a nasty spot when by typical human failing in a non-standard situation, they happen to miss moving all TLs.
Likely the ECAM was displaying messages and the "Retard" call was sounding, but touchdown is a time when attention is directed outside, especially when there's not much runway ahead and it is disappearing fast. This is not a good time for head-down fault diagnosis.