The justices are correct that the 2A does not convey a right to carry a firearm "concealed." However, it clearly does guarantee a right to carry a firearm. Since California doesn't allow people to carry loaded firearms exposed, then not allowing the carry of concealed firearms means there is a total de facto ban on carrying functional firearms for self defense.
Well, technically you are right: the 2A doesn't say anything about the manner of carrying, just that there is a right to bear. The Supreme Court has not ruled on the issue. The 19th Century state cases held that concealed carry could be banned (for reasons of social policy) as long as open carry was allowed. So it could be that a state could choose to go the other way--as Texas did for many years, banning open carry but allowing concealed carry. So I think that the Ninth was wrong in concluding there was no
right to concealed carry, and then refused to rule as to whether there was or was not a right to open carry (despite the fact that the issue was presented to the original panel since California passed a ban on open urban carry while the case was pending). It went the way it did for very political reasons, because it did not want to pen up the state to a "shall issue" law.
In my opinion, the correct answer is that there is a right to carry, and the state may regulate the manner of carry (under current decisions) as long as there is an adequate opportunity for all law-abiding citizens to exercise that right.
The really disgusting thing is that if the open carry ban in urban areas is overruled by Mr. Nichols' case, California will go back to its "open unloaded" law enacted in 1968, and on top of that, the GFSZA makes it practically impossible to carry in any city or town.
To respond to one other comment above, it is legal to open carry in every state or national forest and in most unincorporated areas in the state. A recent law was passed that allows counties to designate unincorporated areas where open carry is banned. Although it is nice to carry if you are afraid you might come across a dangerous animal in the wilderness (yes, there are a few), it will not allow you too carry where one is threatened by the dangerous animals of the urban landscape, which is, for most of us, the only place that really matters.