While I am certainly no expert I do know that some yeast strains such as those used for champagne tolerate higher alcohol levels. Another method is to gradually build the yeast's tolerance up.. after all you are causing them to poison themselves in a matter of speaking. From what I understand you add a bit more fermentable sugar every couple of days and allow the yeast to adjust. If this is what this guy is doing then that accounts for the 12 week fermentation.
Tastes like sherry, eh? duh.. who'd 'ave thought..
Honestly I think the best part about beer as opposed to alternatives (Jim Beam anyone?) is that you can drink a fair amount of the good stuff before you start getting stupid. You have to drink this stuff in shots... hmm.. I think I'll pass.
Interesting stuff though.