I think there are two factors in those numbers that are now influencing future predictions with A-Mart: Voynov and Mitchell.
The Voynov situation has been tossed all over these boards, but realistically unless the case is thrown out Voynov has become a much depreciated asset. Think about it this way, right now he's a $4 million player who's not allowed on the ice with his teammates. He has lost close to a third of the season and, realistically, is unlikely to be on the ice in the foreseeable future. As such, AMart has found himself in essentially the #3 slot on this team ahead of McNabb, Regehr, and Greene. He is invaluable in this mobility and so long as we don't have to see him covering for Doughty or Muzzin long term, he is capable of filling the other $4 million slot on the blueline going forward. Should the Voynov situation end with some kind of criminal conviction, visa issues, and NHL sanction (please Lord, no) it is absolutely essential to have a 27 year old, second pairing defenseman with system experience and 2 cups under his belt on the blueline. The numbers in the article cannot correct for this reality.
The second, and more interesting statistical question, is what happens to AMart now that Mitchell is gone. The language on these boards for years has been that the Kings are an O-D/Stay-at-home pairing team. That undervalues Mitchell's offensive contributions and the role he was able to play as an all-around defenseman who moved up and down the lineup as needed. If we've seen anything with this team over the last few years it's what I refer to as the '40 game adjustment period.' This is what Muzzin went through last season, it's what McNabb is going through now, and I think it will happen to AMart this year as they adjust to new roles up and down the lineup. The defense seem to need about 40 games to adjust and then they take off. I think AMart is being thrown into a new role and will adjust once the D settles down somewhat and he and Regehr really adjust to each other and their minutes. Losing Mitchell and then Voynov forced more adjustment and shuffling than we'd care to admit.
At this point, I will say that the numbers are concerning, but it is a small sample. I think a changing context helps explain them rather than assuming it is a lack of ability on AMart's part. That said, we should look at this again in mid-February and see if there is an upward trend in his overall performance (provided the team doesn't do something like the standard January-February slump where they forget how to score and then turn it on in March which really messes with those kind of short term statistical snapshots). If we see overall improvement for the rest of the season I will argue that we have yet to see AMart's ceiling. For now, I think it is too early to tell.