That's the thinking, yes. Basically, if Apple was going to apply II-style naming to it, they should have classified it as a tiny II.
In the real world, it is an SE class system with an SE architecture and so it got an SE name, which didn't involve an appended "x." as it was on the '030 IIs.
The "rumor" that it was almost the SE/x basically seems to stem from people making up their own reasons as to why it may have been named as it was. Suggesting the "x" was part of a pattern is sort of disingenuous because the SE/30 was literally the second '030-based computer Apple released.
- IIx announced in September 1988
- SE/30 announced January 1989
- IIcx announced March 1989
I think a more likely situation is Apple almost never thought about EOL of their products and what introducing similar successor products should look like, so the II and SE and every subsequent member of their family were named semi-randomly.
Folklore doesn't have any relevant stories, so unless someone has a concrete citation other than just that "SEx" would have looked good next to "IIx" in a product stack, for signifying the addition of an '030, I consider all discussion of the "SEx" to be a case of somebody wishing Apple was less competent than they really were.