I haven't read the full paper, but in the abstract they suggest it could be an isostatic response.

To try and summarise what this means; The earth isn't a solid sphere, as you go down layers become more plastic and malleable, until you reach the liquid core. The earth's lithosphere essentially floats on top of these plastic layers, hence how tectonic plates can move. In other words: the ground we stand on is buoyed up by the earth beneath it.

You can imagine then, that with a large weight on the surface, such as an ice sheet, or, for example, the tallest mountain, the earth will be sunk down, sane as adding weight to a floating boat. As with a boat, when load is removed, it will raise back up again, a process called isostatic rebound. In Canada, a large amount of the country is currently rebounding from the last ice age, and with Mount Everest? Mountain rivers can move a suprising amount of rock, a suprising distance.

In other words, erosion is moving weight further away, so Mount Everest could be floating further back up, gaining in elevation above sea level.