For the most part, discretionary decisions of administrative agencies are given a good deal of deference (google "Chevron deference" for an explanation of certain elements of the doctrine--the oil-company connection is a coincidence).
In light of that deference, it is quite uncommon for a judge to rule an administrative decision "arbitrary and capricious." In that sense, this decision is "activist."
This reasoning is non-sense. Let's see, so essentially you are arguing since a judge normally does not rule administrative agency action as "arbitrary and capricious," and the judge, in doing so here has broken from the norm, then the judge's decision is activist. The fact is, your assumption activism is when a judge's decision does not conform to the norm of what other judges are doing is false. Activism is not defined by scrutinizing whether a judge's decision conforms to what other judges are doing.
What your argument ignores is the fact a judge can break from the norm, declare some agency action as arbitrary and capricious, without constituting as activism. The proper inquiry is not whether the judge has deviated from the norm of what other judges are doing but whether the judge's ruling is consistent with the law, or adheres to the law. When and where a judge's ruling is inconsistent with the law, or does not adhere to the law, then we have activism. Activism is, in part, those instances where a judge's ruling cannot be reconciled with the text of the law. Hence, the fact the judge deviated from the norm is not indicative of whether activism is present with this judge.
We need to know what the law says regarding a judge's review of agency action.
I suspect you have not read this opinion. I suspect you do not know the precise legal standard for evaluating agency action. I suspect you are venturing an uninformed opinion. May I suggest if this is true, then this is a very unwise course of action.
From the opinion itself.
Normally, an agency rule would be arbitrary and capricious if the agency has relied on factors which Congress has not intended it to consider, entirely failed to consider an important aspect of the problem, offered an explanation for its decision that runs counter to the evidence before the agency, or is so implausible that it could not be ascribed to a difference in view or the product of agency expertise. The reviewing court should not attempt itself to make up for such deficiencies.
Then the court went on to say, ""The [Interior Secretary's] Report makes no effort to explicitly justify the moratorium: it does not discuss any irreparable harm that would warrant a suspension of operations, it does not explain how long it would take to implement the recommended safety measures ...A court determining whether some agency action is arbitrary and capricious under the APA makes its decision on the basis of the whole record. (citation omitted) This record consists of the administrative record compiled by the agency in advance of litigation, not any record thereafter constructed in the reviewing court. (citation omitted) Indeed, because the Courts concern is with the rationality of the agencys decision making, post hoc explanations . . . are simply an inadequate basis for the exercise of substantive review of an administrative decision. (citation omitted) "
Essentially, the agency did not make a sufficient evidentiary finding justifying its action. In other words, the agency took action and did not justify it by evidence or a sufficient evidentiary record. Hence, on this basis, I think the judge's decision is a correct one, or at least reasonable.
Ostensibly, this ruling is not activism.