Considering that some colics are mild and resolve on their own, the fact that someone gave alcohol and the horse got better means very very little. There is nothing in alcohol that would serve to break up an impaction, get rid of gas, etc. Alcohol is no better for horses than it is for humans (don't get me wrong, I like a drink now and then ;) ) and is not a cure for colic.
As for mineral oil, it can also help clear up an impaction but we are talking about giving around a liter of mineral oil along with several liters of water to help break up an impaction and move it along. Again, colics can "get better" on their own in some instances depending on what is causing them.
Licensed Veterinary Technician