trawling troll

For fun I posted the question to an online panel of "experts";
"what is the difference between trolling and trawling ?"
....And the official response is;

"a troll is someone who posts rude or offensive messages on a discussion group with the intent of disrupting the discussion or just p***ing everyone off. Trawling, in internet jargon, is sifting through large volumes of data looking for something interesting".

Now I'm confused ? !