I distrust hydrometer (relative density) measurement as an indication of alcohol content of some liquid.
When used to measure consumption of sugar in wort by yeast, as in beer fermentation, then it makes sense.
I am glad that you had fun, and the Korean drink sounds interesting. However, I doubt that a filter could capture enough of anything to produce the results that you observed. The filter would have to gain a tremendous amount of mass!
We did not weigh the filter, nor the liquor poured through it, but, it took a hell of a lot of the filtered stuff to get us anywhere near lit up, and relatively little of the unfiltered stuff to get lit.