At line 81 of raw.c, you are using 6*.../10 as green component factor when creating a thumbnail for the DHG format.
Why 6 and 10 ?
DNG... A forum search might reveal details, that code has evolved, it wasn't always 0.6. There is no color matrix or white balance applied to the thumbnail, so I suppose it's just an attempt to adjust the colors so that they're reasonably tolerable on most cameras.
And are you using both green component of the Bayer cross?
No. It's supposed to be very simple and fast. It just gets a few pixels here and there and scales them around a bit according to a common gamma curve to cook up rgb pixels that are close enough.