What is the ceiling altitude for the Airbus A320?
This question is a bit more generic. Ceiling altitude depends on many things such as (environmental conditions, engines operative, a/c aerodynamic characteristics, e.t.c), each factor by itself and in combination, can affect the ceiling altitude. You can get an idea and some definition from here: https://en.wikipedia.org/wiki/Ceiling_(aeronautics) .


  For most of the A319/A320/A321 aircrafts Maximum Certified
  Altitude according to FCOM is FL391 considering (2 engines operative
  and environmental allowing.)


Now according to FCOM DSC-22_20-50-10-28, (controls and indications) you can find the MCDU page, 

REC MAX:
This field displays the recommended maximum altitude (in magenta), that is computed based on the current gross weight and temperature, and assuming that the anti-ice is off (Refer to QRH graphs, if icing conditions are expected). It provides the aircraft with a 0.3 g buffet margin, a minimum rate of climb at MAX CL thrust, and level flight at MAX CRZ thrust. This field is limited to FL 398.
If one engine is out, this field displays the recommended maximum engine-out altitude, that is computed based on the long-range cruise speed and assuming that anti-ice is off.



Note: The OPT or REC MAX field may display a value up to
FL 398. However, the current aircraft’s maximum certified altitude is 39 100 ft. Disregard the OPT or REC MAX value, if it exceeds FL 391.

Now for entertainment system, (again according to the books), reads and display data taken from the FMGC. 

One scenario is the input from the pilots, in MCDU was the displayed LVL, and subsequently in the entertainment system, the displayed LVL
was that (after the CRUISE phase), even though the actual altitude was
different that the displayed.But again it's impossible to insert an altitude above the value of "FL398" MCDU says "ENTRY OUT OF RANGE". 


  So the conclusion As kevin said already, possibly wrong data were
  displayed.