"Purported Appeal" transmuted into a writ petition

You know how the caption of every decision there's an intro line that says something like "APPEAL [or ORIGINAL PROCEEDING] from an order [or judgment] of the X Superior Court. John Doe, Judge. Affirmed. [or Reversed]"? Basically, this is the line you skip over, unless you want to see who the trial judge was. Well, here's a new twist on that you probably don't see much:

PURPORTED APPEAL from a judgment of the Superior Court of Los Angeles County, James C. Chalfant, Judge. Treated as petition for writ of mandate. Petition granted.