The Chargers have been doing this regularly. Its because they got sick and tired of Raider fans coming in from Northern Cali because, well, Charger fans just don't turn out all that often.
The City of San Diego has regularly had to buy up tickets from the team to ensure that the team wasn't blacked out. That may not have happened this year, but it happened regularly from 2002-2005.
San Diego is a city that has a LOT of turnover. There are TONS of people who go to San Diego for a year or two and then leave. Some go there and stay forever, but they root for the team they rooted for prevously. My brother is a perfect example. He has a group of about 15-20 friends who get together to watch the games. Most of them are from New England.
There are also 1-2 New England Sports Bars in San Diego.
