ATCast
Hello Robini,
It is not uncommon for the entertainment system to be incorrect. I recently travelled on an A340 where I noted a similar error. It turned out that for a certain unit (can't remember whether it was kph, kts or mph) it added the headwind to the airspeed to obtain groundspeed.
When I selected the other units, the headwind was correctly subtracted from the airspeed to obtain groundspeed.
Rgrds,
ATCast