Totally agree. The RICO case is a criminal case, and the decision that McAfee made was a decision in a misconduct hearing, not a criminal matter.
Preponderance is a perfectly reasonable standard for that proceeding. What I found a odd was using the term "conclusive", which is not needed when preponderance is the standard. That is a term more appropriate when reasonable doubt is the standard.
You can take the word "conclusively" out and just say "neither side was able to establish by a preponderance of the evidence when the relationship evolved into a romantic one."
That serves the same purpose, and it doesn't leave the impression that a preponderance standard requires "conclusive" evidence.
McAfee is a very careful speaker- he doesn't usually say things that he doesn't need to say. It just jumped out at me because it seemed out of context for the standard being applied.