ok if you found grass in his poop than it means he ate grass
dogs eat grass to calm there stomachs like we take meds they just eat some grass it is most likely nothing to worry about but my mom is a vet and if your concerned or it is a continuos thing call your vet.
hope this helps
No, this does not mean he doesn't get enough nutrition. It just means he has been eating grass which is common in a lot of dogs. You shouldn't worry just keep him away from grass eating.