Idk, in the example "a built racecar engine" one could imagine that instead of running CNC machines all day long to make pistons, replacing tools for wear periodically, a machinist could take a brand new end mill, make some initial test cuts and validate the dimensions, then make the final part and look it all over with the CMM or other tools. You could, by paying extra attention to each part, make a more precise part than something being made on an assembly line where things are not double checked quite so meticulously, for basic efficiency reasons.
Like I assume that by the same definition of "hand made" as the racecar engine, we would consider NASA rovers to be hand made. And they are made to a very high precision. We could consider whether SpaceX Engines have ever been "hand made" and how the quality of those relates to production engines (tho in this case, production engines must have rigorous validation of basically every component I would imagine, so the factory perhaps meets or could even exceed hand production runs in quality).
But I would not say it needs to be a hard and fast rule.