Everyone agrees on the result, but the California Supreme Court splits three different ways as to why.
This is another big case (the other being Wells) in which the Court holds that anonymous tips are sufficient to authorize the police to detain someone. Wells was about a drunk driving tip; this one's about a person with a gun. There was a dissent in Wells, but this time, with respect to the result here, the Court is unanimous. It's another case that, as a practical matter, both increases the authority of the police to combat crime as well as provides a powerful tool for individuals to harass their enemies. Just report to the cops that they're driving drunk or have a gun and watch the guns-drawn fun.
The fact that everyone agrees on the result here doesn't mean there's substantial agreement, and Justice Kennard writes a separate concurrence, as does Justice Werdegar (joined by Justice Moreno), to explain their disagreement with many of the arguments adopted by the majority. But that's not too surprising, since all three dissented in Wells. Justice Baxter, who didn't participate in Wells, is in the majority, but that's not too surprising as well.
Different perspectives on anonymous calls, but the result is that, at least in California, they authorize a seizure.