My understanding is that the felony requires that the

Falsification of business records be intended to conceal evidence of another crime. The indictment didn’t specify the crime, but the DA has suggested that the payment was an unreported campaign expenditure. The feds looked at and passed on prosecuting that, likely because they felt they couldnt prove that the cover up of the affair was for campaign purposes as opposed to, for example, marital purposes.

Without the felony charge it sounds like the misdemeanor case is pretty tight, but not the type of thing that gets prosecuted.