Machine Gunners... IAB or GAB ???

[Hessian]

I just picked up a super neat grouping for a DAK officer (see thread here)

But one question nags me... he has an "M" on his shoulderboards which means Machine guns... but was awarded the General Assault Badge and not the Infantry Assault Badge. Why would this happen? Were machine gunners not considered Infantry?

And I know he was always a Machine gunner so its not like he was first awarded the GAB for something else. The GAB was his only assault badge.

Any help on this is appreciated.

Thanks
Duke