I don't think the surface is porous so much as you didn't clean the pan and left capsaicin behind in it. You could try this with other materials - can you elimi

I don't think the surface is porous so much as you didn't clean the pan and left capsaicin behind in it. You could try this with other materials - can you eliminate all the spice from stainless or glass without using soap as a surfactant? It's fine to wash cast iron with soap, and when you're working with spicy things and others use the pan, you really ought to consider it. Even if you don't usually wash your pan.