$100 is certainly a bit on the high side, but I live somewhere where mixed drinks can cost $12 at nicer bars. Have 5 of those (not unreasonable if you go out around 6pm and stay out until 1-2am), throw in $15 worth of food (as the author mentioned), and you're up to $75. I tend not to go to bars that charge cover, but that could be anywhere from $5-$20, though usually if you arrive at a particular bar before 10pm or so, there's no cover charge.

So $100 may be slightly hyperbolic, but it can happen without too much difficulty, depending on your tastes. I happen to really enjoy Scotch, and whiskey in general. Go to a bar with a selection of mid- to high-end stuff, and that can run you $20+ per pour. I tend to drink them quite a bit slower, though.

But agreed that this doesn't answer why he doesn't drink at all, but is more an answer to the question of why he doesn't "go out drinking".