This rule has been around forever. A pitcher has to face one batter! Only exception is pitcher on mound getting injured. This rule is pretty clear.
An offense can pinch-hit as much as they want. The pitcher must face at least one at-bat!
How the F can the umpire blow this one? For me, this is much bigger than the Angel Hernandez HR call. The HR call has some judgment involved. The Astros pitcher fiasco is a rule interpretation. MLB got this one wrong, and I'm outraged.