I cannot belive that he/she would use a different thickness of wall board regardless of its color within the house.
Consider that all wallboard the same thickness, is wider in the inner edges that on the long side edges, this is for a good butt up and for taping. So a patch on the sides long sides of a piece will need extra compound because of the taper sides.
But, green board and reg board side by side will tape and prime and you will not see the difference unless its different thickness's patched or butted alongside each other.
I guess that the home supplies is void of patching or left over reg drywall so he/she is improvising. If more patches around and no reg rock go out and buy some more for patching purposes.