Last week, our cable company ran that test FOUR times in one afternoon. Since 9-11, there have been more of these tests. I also suspect that they tend to run more if the news is bad. I have cable on my PC and I HATE when that thing goes off!
This sounds to me like your cable company is having trouble with its EAS equipment. (How many subscribers does your cable system have? Systems with less than 10,000 subscribers did not have to join the EAS alert system until just this month. So if it's a small cable system, they're probably just still tweaking the equipment.)
I would suggest just calling your cable company, asking to speak to the chief engineer, and just ask him point-blank what's up. Or you could email the FCC's EAS department and ask them if there's been an order to increase the tests: eas@fcc.gov.