The article points to a few of the more recent ballot initiatives as helping create this change (though I don't personally give as much credit to them as the paper does) and also notes one other thing -- the governor, Senate and Assembly are all Democratic, and by significant margins. It's hard for me to imagine that this latter can't help but be the most significant factor in ending gridlock...by far.
As I said, they do mention it a few times, but it comes across as almost a throwaway. Most of the article concerns the impact of the ballot initiatives. One Proposition was that the strict term-limit law was eased, which certainly helps allow for more experienced lawmakers, rather than a bunch of newbies trying to elbow their way around. The other initative was that the top two vote-getters in primaries now face each other in the general election, regardless of party.
I do understand their point that this has freed up candidates from just having to win the support of partisan party interests and forces them to take a more general, moderate outlook. The article notes how, as a result of this, Republicans have helped pass some more-traditional liberal issues, and Democrats have voted down some more-traditional, business-related (or Republican) bills. That sounds valid, and it may be, but all of the people they quote as appreciating this "freedom" are Republicans, who suggest that they now no longer have to appease the extreme far right of their party. But since the article also notes that it appears this "open primary" system has largely benefit Democrats, that would contradict the impact the "open primary" might have had on the lack of acrimony, if mainly (or only) Republicans are saying they are now able to move more to the center.
I'm sure it's had some impact. But there could be other factors at play in moderate actions -- most notably, California had a serious budget deficit that needed to be addressed. (And was. As mentioned, the huge budget deficit has turned into a surplus.) That could easily have been the motivating factor. Necessity, after all, is the Mother of Invention. In the end, after all, seriously, how could "one party controls all three houses" not be the overriding difference in removing "gridlock" and creating unity?
Still, it's a thoughtful article (even if I'm sure sure of all the conclusions), and a good look at a state government working, and does point to how having one party in control and acting responsibly can have a major impact.
And in this case, that one party is the Democrats.