Earlier quoted context omitted.
We use bacon fat or avocado oil. For cleaning, we use a Lodge plastic scraper if needed. And we never use soap. We wash our cast iron with about 2TBSP of kosher salt. Just dry on the pan, maybe a few drops of water, rub with a paper towel. Removes all the food debris while protecting the seasoning. Rinse the salt out with some water then dry or deglaze immediately.
I doubt that. I do more or less as you do but, after that process, if I take a clean towel and rub it against the "clean" surface, it invariably comes back with a distinct brown color. That brown color doesn't look like "clean" to me, it's more like burnt oil... I'd expect my towel to be 100% clean if that "seasoning" was working as advertised...
Yes, it is effectively burnt oil and you probably shouldn't eat too much of it, but it will give steaks for instance a great crust and I think it adds a bit of flavor as well.