I don't think the purpose was primarily military-related. The US's GPS system can be jammed as is, and I don't see any reason why this system would be any different. GPS satellites are very far up in the atmosphere and thus produce a very weak signal to near-earth. This isn't just a theoretical attack: a few years ago, a truck driver with a GPS jammer accidentally jammed the GPSs of planes above him landing at Newark [1].
I think it's more a matter of national pride issue: to show the world that China doesn't have to rely on the US for technology. Russia's GLONASS system (briefly referenced in the article) is more or less the same thing. The good news is that this system, like GLONASS, will likely improve positioning speed / reliability, since there will be more navigation satellites in the sky. Already, receivers can tie GLONASS and GPS together; it's only a matter of time before Beidou is integrated as well.