User blog comment:ArtsAndAnime888/The future of Fairy Tail- NaLu/@comment-7418318-20140730200928/@comment-76.161.172.226-20140801142103

Probably more importantly, people ignore that Mashima was asked a hypothetical question of "If Natsu and Lucy had a kid, what would their name be?"

Mashima merely came up with a name on the spot that combined their names (na)tsu and ru(shi), much the same way he combined (a)lazk and bi(suka)'s names to get the name of their daughter.

Nothing about the question or Mashima's response implied that they definitely would have a kid. He was just asked to come up with a name for a hypothetical kid on the fly and did so.