Correct, the recidivism rate for sexual offenses is generally lower than for the general criminal population in the United States, although the rate calculated varies a lot based on the metric and type of offense. See here . Quoting from that page:

"Marshall and Barbaree (1990) found in their review of studies that the recidivism rate for specific types of offenders varied:

* Incest offenders ranged between 4 and 10 percent.
* Rapists ranged between 7 and 35 percent.
* Child molesters with female victims ranged between 10 and 29 percent.
* Child molesters with male victims ranged between 13 and 40 percent.
* Exhibitionists ranged between 41 and 71 percent."

This is in contrast to base rates for reoffense in the US for general crimes which ranges from around 40% to 60% depending on the metric see here.

This isn't the only example where recidivism rates for specific types of people have been poorly described. There's been a large deal made by certain political groups that about 20% of people released from Gitmo went on to fight the US.

Note also that in Western Europe recividism for the general criminal population is lower. I believe that the recidivism rate for sexual offenses does not seem to correspondingly drop, but I don't have a citation for that.

Edit: Last claim may be wrong, this article suggests that at least in the UK recidivism rates are close to those in the US for the general criminal population.