IMO Growlithe is actually a kinda bad example because Arcanine can run Mixed set really well, as its base SAtk is 100, only 10 points less than its base 110 Atk.
However, it doesn't affect the point of the guide, so if you don't want to change it, it's fine.
But one thing that I think should be changed, is your reasoning for why -SAtk nature that's not Adamant or Jolly is considered neutral instead of good.
The way you worded it, it sounds like all natures with -SAtk should be considered good nature for Growlithe.
Perhaps its better to say "Natures which reduces SpAtk but doesn't increase Atk or Speed are considered neutral because Growlithe needs Attack or Speed boost more than a Defense or SpDef boost". That way you basically tell people that Impish and Careful are okay, but not as good as Adamant or Jolly.