Um, he secretly met with them BEFORE testifying in Congress. Unless, of course, he put out statements immediately after the Parisian meetings that said he just met with the NVA.
Telling Congress about it one year later doesn't mean he didn't meet with them secretly the previous year.
His first meeting in Paris was end of May, 1970. His testimony before the Senate committee was April 22, 1971. He then met with the North Vietnamese in Paris sometime in the summer of 1971. He's never admitted to that meeting as far as know, and it only came to light with Nicosia's review of FBI docs. Newt mentioned a third visit, but we don't have record of that one, as far as I know.