It seems to be doing some kind of tone mapping/pseudo-HDR thing.
Here's what a linearly depicted properly exposed image looks like:
Here's a thumbnail preview of the same image with a typical light curve added:
Everything we do with raw images captured using an imaging sensor that is linear in its response curve to light is "some kind of tone mapping/pseudo-HDR thing." That's what an adjustment to a light curve is! We're altering the relative difference in brightness between areas where more or less light was recorded when the image was taken.
This was also the case in the film era, except that the film emulsions themselves were designed to be more or less contrasty and to shape the curves at both ends of the dynamic range flatter or steeper.
As Ansel Adams perfected in the development of his 'Zone System', altering the exposure time and compensating with a longer or shorter development time alters the shape of the response curve for the same film emulsion. But Adams didn't stop there. He dodged and burned when making his prints by blocking certain areas of the light shining through his negative in the enlarger. Areas of the photosensitive paper that got light from the enlarger for less time printed lighter and were said to be "dodged." Areas of the paper that got light from the enlarger for more time printed darker and were said to be "burned."
Moving the "Shadows" slider in ACR raises the brightness of the dimmest parts of the image without doing the same to the mid-tones and highlights. It does so in a similar manner to the way Adams (and everyone who followed him) would reduce the contrast of his images by altering his exposure and development times so that there was not as great a difference between the darkest parts and the rest of the image.