An advertising gimmick.
The Artois reasoning is that holding the glass by the stem means the heat from your hand doesn't warm the glass. However, a full pint is getting a bit heavy and unbalanced to lift by the stem, so most people would probably just lift it by the body of the glass as usual, thus defeating the purpose!
Another guess is that the shape with the least surface area for a given volume is a sphere. The less surface area there is, the less warming there is from the surrounding air. The Artois chalice glass is approaching a spherical shape, so should keep the lager cooler than a straight-sided glass would.
If this is their reasoning, then note that pubs already have glasses like this, namely those tulip glasses that they serve half pints in, shaped like wine goblets.
This all makes the Artois claim a bit of a red herring, i.e., nothing new.