Based on your analysis.......'Creatures Of The Night' was released in '82. It's the '80s, metal is already solidly off the ground, you've got several albums from Maiden, Priest, etc. So........looks to me like that would just constitute some kind of trend following. They heard Priest or Maiden and thought "hey that's cool." To stay alive, pop bands have to change with the times. For KISS, they have so many 70's fanatics that they don't need to obviously......but....You say that 'Creatures of the Night' is kind of metal. Did 'Creatures Of The Night' represent a complete change in sound for them? Are they still doing the same stuff? Because......just my educated guess would be that they went back to the old style, maybe in the early 90's they had some "grunge" sounding songs on their albums, but that wouldn't mean they're grunge either.
Even IF that album was slightly metal (I'll listen to it), you can't argue that kiss are a heavy metal band based off of one album in the 80's.