When one is creating a headline and one can choose between two words, using the one that isn't confusingly ambiguous is usually the better choice.

My assumption, which dates back to the first time I encountered the word "troll" in its usenet sense, was that it derived from exactly that metaphor.

Trolling for a reaction. Spreading out some chum, setting the line, seeing who bites.

Yep indeed. From the Jargon File:

> Derives from the phrase “trolling for newbies” which in turn comes from mainstream “trolling”, a style of fishing in which one trails bait through a likely spot hoping for a bite.

http://catb.org/jargon/html/T/troll.html

You are definitely confusing the word troll, "A mythical, cave-dwelling being depicted in folklore as either a giant or a dwarf, typically having a very ugly appearance." (OED), with the word trawl: "1 an act of fishing with a trawl net or seine or 2. a thorough search". The parent comment actually mentioned trawling in his post, too, as a alternative Ars could've used.

I am definitely not confusing troll for trawl. Look it up, the definition I gave is a valid one for "troll".

You found troll(1) in the OED.

Now find troll(2).