Imo, calculated fg doesnt mean a lot to me. Even with a yeast that attenuates 70%, a large pitch can easily take it to 80% or more. Recipe builders (at least brewers friend) dont take mash temp into consideration when determining fg. I agree that your ingredients, processes, and other factors can lead to that lower fg, but for you to say something went wrong and his process is bad is not correct. First you said it was infected and the recipe couldnt get that low, now you say it might be his recipe or processes/equipment. Instead of telling someone they are wrong and produced a beer the wrong way, we should be encouraging them to examine their brewday and learn. Maybe mash higher next time if you the same yeast, or use a yeast that doesnt attenuate so much. I can certainly tell you that my beer tastes fantastic and i imagine his will as well. Thats not a fail, just a different than expected outcome.