From NASA: Potentially, A Breakthrough (Understatement of The Century)

[drm604]

5. Where did you get the idea that no energy was applied to the "box"?

From the PDF you linked to:

Approximately 30-50 micro-Newtons of
thrust were recorded from an
electric propulsion test article
consisting primarily of a radio frequency (RF) reson
ant cavity excited at approximately 935 megahertz.

They refer to is as "electric propulsion" implying that electricity was involved. Radio frequency energy was applied, which means that energy was applied.

Reactionless electric propulsion would be a major breakthrough, but it wouldn't be free propulsion. You'd still need an energy supply of some kind.