It's probably cuz he bets more confidently on the net. Since it doesn't seem like real money, it's easy to make higher bets than you would in a casino. If the cards are in your favor, you CAN win a lot of money. I once won $10k in a night playing $100 a hand on line...then one every night for a week...I don't have to tell you that the tide turned hard.....but the tide DID turn and it will turn on your friend. I think most of the people who lost big money in real and on line casinos are those who, at one time, had a lucky streak, won a jackpot or picked a Randizzle like streak of winners. Your friend should count his blessings, but he needs to realize this gravy train will not continue forever..Although odds in blackjack can be better than in some games, the odds still favor the house and on a computer...well, it's anyone's guess how they can rig those things.
Online Blackjack often has rules more favorable to the player than physical casinos. Rules like doubling on any number, surrender, re-splitting aces, drawing to split aces, etc...
You can see the effect of variable rules here:
http://wizardofodds.com/blackjack (scroll down to Rule Variations)
The house edge can be as low as 0.5%. Combine that with the ability to play as fast as you want, and blackjack being high variance, and you can get very substantial win streaks online; versus off-line you wouldn't play nearly enough hands.
There are a few places online where you may be able to count cards, but I doubt that's the story here.
It's still EV negative, but the common wisdom that physical casinos are a better deal than online casinos is patently false. (With the only exception of playing poker against drunk fish).
