I recall this exact discussion happening at various times over the last few decades.
I agree that the verb comes from fishing, but with respect to fishing, nobody calls a person who trolls, a "troll." If the noun came strictly from the fishing use of the word, the people engaged in trolling would be "Trollers," not "Trolls."
I think both etymologies are in play, one for the verb, another for the noun. It could have been that it began with the verb, and somebody punned "Is someone who trolls, a troll?" and that stuck.
But what makes the noun work is very definitely the association with the mythological trolls who are unhelpful to humans.
“Trolling is a method of fishing where one or more fishing lines, baited with lures or bait fish, are drawn through the water.”