There's nothing inherently offensive about the phrase "used to troll". What is being expressed is that a specific keyword (unstated in your question) is commonly used in the activity of trolling.
Wikipedia describes trolling as
In Internet slang, a troll is a person who starts flame wars or intentionally upsets people on the Internet by posting inflammatory and digressive,1 extraneous, or off-topic messages in an online community (such as a newsgroup, forum, chat room, or blog) with the intent of provoking readers into displaying emotional responses and normalizing tangential discussion, either for the troll's amusement or a specific gain.
The word or phrase that got "caught" by the algorithm was one that apparently appeared commonly in messages from trolls and less common in "legitimate" messages.
Merriam-Webster also provides a definition of trolling:
2a : to antagonize (others) online by deliberately posting inflammatory, irrelevant, or offensive comments or other disruptive content