Surprisingly, this was not a personal bet that Buffett placed, which we've seen him do in the past. Instead, Berkshire Hathaway was on the hook for about $30 million had France won the World Cup! The fact that he used company money to place the bet suggests a seriousness to the wager that would not be present had this been a fun, personal side-bet.
So why would Buffett be taking serious sports bets of this nature, when there is a whole industry dedicated to working out the odds that will result in maximum profits? It's possible that this particular bet was so large that no casino would take it, and so Buffett was able to earn a premium on the regular odds for offering such a handsome payout.
On the other hand, maybe the Oracle of Omaha knew something about the French team that allowed him to offer better odds than the bookmakers. After all, not only did the French get ousted from the tournament early, but they completely embarrassed themselves as well. The actions of the players against their coach would normally seem astonishing, until you consider that their coach makes some of his personnel decisions based on astrology! Buffett has a lot of experience making money off of those practicing astrology, which is a trading "tool" that was often utilized by the earliest technical analysts.
More on the story is available here.
Disclosure: Author has no position in the fortunes of any World Cup team