My guess;
The heading you see as a yellow line at your ND is magnetic. So when you are looking at this tiny wind arrow at the upper left of your ND you will compare it with you magnetic heading hence it is in magnetic.
The numbers however are usually used for planning purposes. Which you either insert into your FMGC or send to ATC when requested. So these winds need to be used as true heading. Or you will need to convert it to true heading every time you enter those winds into FMGC or send wind reports to ATCs.
Regards,
Guclu