[narwan]

It's a side-effect of the reduction in lethality of artillery against AFV's. MMG's and'HMG's have a splash zone like heavy HE rounds do and the game treats them the same with regards to splash effects. Where rounds used to hit AFV's and have a chance to do full penetration in hexes in the spalsh zone, now they sometimes/often only shower the target with 'splinters'. That gives suppression, can strip a vehicle from riders and do damage if it hits an unarmored surface.
The MG's use the same mechanic and give you the same message. I agree it reads a bit odd, perhaps this will be tweaked later but it is only the text that is off for mg's (and hence only a very minor issue).

Narwan