Smoking oil and cooking oil are different. The butane method extracts the oils naturally occuring in the weed then evaporates leaving only weed oil.. High % of THC and you can smoke it.

Cooking oil or butter are used to extract the THC from the weed so you can cook with it. You just heat up the oil/butter and throw some weed in there. Then filter out the solids. Its still mostly cooking oil or butter though, you can't (at least I won't) smoke it.