At the time, people were saying that he was flying home from DC, and that Article I Section 6 of the Constitution protects Congressmen from arrest when traveling to and from Congress.
They shall in all Cases, except Treason, Felony and Breach of the Peace, be privileged from Arrest during their Attendance at the Session of their respective Houses, and in going to and returning from the same; and for any Speech or Debate in either House, they shall not be questioned in any other Place.
One could argue that being arrested for public indecency is a "Breach of the Peace."
-PJ
I guess it could be. But that clause reads so weirdly today. They could be arrested for selling their country out, or for a murder (or in their day a horse theft), or... for a loud party. The sublime next to the ridiculous.