From the article:
"When I first noticed this disparity about thirty years ago..."
Could be his information is simply out-of-date and he hasn't thought to re-assess the current context.
Tilt: rather than asking what bare attention means, let's ask the author of the article in question what he thinks it means:
"...bare attention corresponds much more closely to the Pali term manasikara..."
(In Sammasati, An Exposition of Right Mindfulness by Ven. P. A. Payutto:
"To demonstrate the process involved as a sequence of events, one could say that when sati brings an object to mind and lays it down in full view of the mind, yoniso-manasikara, as it were, picks it up and manipulates it in such a way that pañña may scrutinize it and then deal with it effectively.")
So what is the author's problem?
"The cultivation of bare attention is valuable in many ways, and there’s a rapidly growing body of research on its benefits for both psychological and physiological disorders. But it’s incorrect to equate that with mindfulness, and an even greater error to think that’s all there is to vipassana."
It seems he might agree with Ven. Payutto's quote, above. Logically we would say that bare attention (yoniso-manasikara) is a necessary but insufficient component of the vipassana process. But wait!
"So bare attention doesn’t by any means capture the complete significance of vipassana, but represents only the initial phase in the meditative development of right mindfulness." (emphasis added)
(Payutto disagrees here, as yoniso-manasikara is not initial:
"A comparison may be made to someone in a rowing boat out on a choppy river, picking flowers or water greens. Firstly, that person ties up the boat or anchors it in such a way that it will remain stationary at the spot where the plants grow. Then with one hand he grasps hold of the stems, gathers them together and exposes them as conveniently as possible for harvesting. With the other hand, using the tool he has prepared for the job, he cuts them off. Sati may be compared to the anchor which stabilized the boat, enabling the man to remain within reach of the plants. The boat, held stationary at a given spot, may be compared to the mind. The hand which grasps the plant stems and holds them in a convenient way is like yoniso-manasikara. The other hand, using a sharp tool to cut off the stems, is like pañña.")
Aside from differing on the ordinal structure, both agree that yoniso-manasikara is a component and not, in and of itself, the whole of vipassana. So now we have a rubric: a vipassana meditation teacher will be subject to the author's critique if they teach only yoniso-manasikara to the exclusion of other sammasati path factors.
Turns out we simply need to determine if this rubric applies to one vipassana teacher or another, or we have to deny the rubric as being either subtly or critically flawed.