Build the Alps - Pulling or Pushing?

A correspondent has brought THIS PAPER to my attention. We used to think that the Alps were built by the Adriatic plate pushing against the Eurasian one, pushing lots of stuff to create the mountains.

But the seismicity of the Alps is characteristic of expansion, not of the compression that you would expect. The paper tries to explain this and other phenomena.

The explanation given that, as the Adriatic plate, especially the continental part abutted the Eurasian plate (30 Ma ago), the upper, lighter, crust of Eurasia, separated from the lower, denser mantle. Being lighter it surged upwards (no doubt, at a suitably stately pace) to form the Alps.

The sinking of the lithosphere sucks the Adriatic plate northwards.

Reading the article may help to understand it - I am struggling with it. Where do these wonderful nappes come in?

The Journal article may help but you need some form of subscription to access. THIS gives the abstract. But a "high-resolution, rheologically consistent, two-dimensional visco-elasto-plastic thermo-mechanical numerical model" seems a bit above my pay grade!