Book also says, bohemica reddens less than Macrolepiota rhacodes, which isnt terribly helpful if you have never found a Macrolepiota rhacodes.
But judging by your description of the taste it seems something wasnt right. The germans used to say a shaggy parasol tasted similar to a veal schnitzel, which isnt much help as veal is virtually unobtainable in this country as well.
I never thought they tasted like veal but i smoke 20 a day so that aint reliable, and the grass thing, well fungi grow in such a hidden way that the green pasture could have been pinewood in recent history.
Putting the taste and the grass together my guess without seeing the thing in situ is that you got one of the bohemicas, note these are not poisonous, just not tasty
Tant