I think they changed the dashboard face on fiestas after a certain age, and I believe the st was introduced when they did the facelift, hence the soft dashboard front.
I may be completely wrong however.
Think it was 06 when the facelift (mk6.5) as some called it, was introduced. ST's came before the facelift, 05 iirc.
As for the material, think its just some kinda soft touch plastic? My mate used to have a Zetec S 06 with the soft dash, just been a while since he had it so I can't remember fully