Actual conversation I had last week with my daughter:
"Dad, did you cook something spicy in the skillet" (I have a cast iron skillet and normally am the only person who uses it)
"Yes, I made a sauce from chilis that was much too spicy, and used the skillet to cook the sauce down".
"Well, can you let me know next time, because I just made very spicy bacon!"
I normally only wipe down my cast iron skillet rather than cleaning it, and I think the metal is porous (even after seasoned), because I could still get a hint of spice on my finger from touching the cast iron surface.
Maybe put a half a cup to a cup of evoo and warm up the oil, swirling it around next time? Then you can let it cool down and maybe use this to solidify the oil?
What you want is a high iodine value. Both avocado and olive oil have low iodine values, and they’re premium oils, so doubly wasteful for cast iron seasoning.
I think the idea is the higher the smoke point the easier it is to bring the oil to a high temperature to get it to polymerize. I don't know if this is true, as my pan came preseasoned and then I mainly add to that by carbonizing previous bits.
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.
Capsaicin dissolves in alcohol, so I tend to wipe everything down with 70% IPA minimum with a paper towel before sending it into the dish washer.