Newt Gingrich may not have meant it as a laugh line when he declared he was simply in "the private sector," but the audience did. Why? Maybe because so much of his private sector work involved indirectly pocketing taxpayer dollars.
Gingrich was paid to help drug companies win new subsidies through Medicare. Gingrich was paid to protect and expand ethanol subsidies. Gingrich was paid to help protect Freddie Mac, which, thanks in part to that protection, blew up and pocketed millions in taxpayer bailouts.
In all of these cases, Gingrich was profiting, at taxpayer expense, by increasing the size of government. You could call that the "private sector," or "free enterprise," as Gingrich does. Or you could use those phrases more precisely.