The issue of Mannock's hatred of Germans is well documented and supported by several pilots who knew him personally. And most of these pilots thought the world of Mannock.
Ira Jones is a good example. To him Mannock was the best combat leader he flew with, and a outstanding fellow to boot. Therefore it's most unlikely that he would print something that is likely to be considered less than deserving. And in point of fact Ira attributes his own 'hate' of the hun to Mannocks influence, which he fully endorsed, in both World Wars.