According to National Journal here:
Naval expert Norman Polmar, a long-time consultant to the Navy and Pentagon, said he believes the missile was almost certainly launched by the US military. “From the video it’s clearly a land- or sea-launched ballistic missile, and it couldn’t have come from a French or British submarine, because they are only deployed in the Atlantic and Mediterranean,” he told National Journal. “Chinese submarines have never ventured farther east than Hawaii, nor have they ever successfully test fired a ballistic missile. That only leaves the Russians, but for the life of me I can’t fathom why Moscow would have a submarine sail 5,000 miles to launch a missile off the coast of California.”
I can fathom why a North Korean submarine would do it, or a Chinese submarine, especially just ahead of Obama's arrival in Seoul for the G-20 meeting.
But the capability question is still there in both cases.
Do the North Koreans have a blue water submarine, let alone the technology?
Do the Chinese have the technology?
And why would the US government lie about a test of its own?