A Macbook Pro is made from aluminium. Most other laptops are plastic. Metal-on-metal scratching would be quite different to metal-on-plastic, so I'd say it's relevant.

Why is it quite different? Is it that aluminium is a poor material for a surface likely to suffer repeated abrasions?

I think it's the fingernails on chalkboard effect of similar hardness. Soft plastic against hard metal doesn't quite screech the same way.

Maybe he doesn't like the noise it makes...

"...a pretty boring business-to-business industrial sector"

The outcome was predictable from reading the first sentence. This is not a story about any failure of Facebook, it's a story about not understanding how to market to an appropriate demographic.