Reb Moshe seems to be assuming there are no platonic relationships between members of opposite genders. If you read the tshuva and related ones, he is fairly clear that the issur of talking devarim bteilim to women is that of an intimate nature, as a prelude to forbidden acts. Asking how’s the weather is not what is meant. In addition, his chidush that mere talking is d’oraisa is certainly not pashut pshat in the Rambam or Maggid Mishna there.
But if one believes there are no platonic relationships or friendships, then this will eventually lead to forbidden talk.