I've ordered a peperoni pizza in several countries in Europe and I've never herd this.

Würst is the German word for sausage, and while I can easily imagine Germans saying peperoni-würst, I can't imagine this being common outside of Germany.

Pepperoni is an Italian style sausage, where the word and branding was made by Italian immigrants in the US.

If you want to order a peperoni pizza in Europe, you might need to know what they call them there, even if they are excellent in speaking English.

In Italy you would order a salame pizza. In eastern Europe, without speaking the local language, I've had to order a sausage pizza, and in any country more influenced by American culture, peperoni pizza is what you order. I haven't ordered pizza in Germany, but I will probsbly do that now the next time.