How is an outside ethics panel going to affect their working conditions? The people on the panel don't have any say on employees' pay, promotions, disciplinary actions, assignments, or anything else that might affect their working conditions.
The idea was to have some people from outside the company look at the tech and its potential hazards and provide some input on the ethics of developing and deploying it. People inside the company said, No, we don't want that particular viewpoint to have a seat at the table on this outside committee. The ethics panel had nothing at all to do with their working conditions.
The employees of google would then be expected to produce and maintain these projects. That's their work. At the least, they're expected to share a roof with these projects, and profits from the work they do could be spent on these other projects, or vice-versa.
'Working conditions' includes those things I mentioned: pay, promotions, hours, etc.
The AI ethics panel may or may not have led to a change in the scope of 'work.' We'll never know, because the panel was disbanded. Presumably Google is now making decisions about future AI work without the benefit of the ethics panel.
In any event, organizing a protest against the composition of this outside panel that had exactly zero power to change Google employees' working conditions does not fall under the NLRA. Apparently Meredith Whittaker was counseled along the same lines, which is why she resigned after trying to pressure Google into changing their decision by using publicity via the press, rather than suing under the NLRA.