The option was likely put their for Twitch to gather analytics on how many people requesting refunds are doing it for that purpose. Gives them insight by separating those into another category rather than people doing it for that reason simply putting "it was an accident" or something else as their explanation, which makes it difficult to tell them apart from legitimate reasons.

Not sure exactly how gathering that info would be useful, but could just be to see how much of an impact those types of refunds are making overall and helping decide what could be reasonably done to combat that without removing or restricting refunds in a user-hostile way.

Just my thoughts on the spot. Others commenting seem to agree that it was already being done before and this option in the refund menu wouldn't change the frequency of it happening much. But also bringing attention to it could encourage more people to try and do that to troll. Either way I'd say there's probably an angle that Twitch is taking to simply gather data on how the feature is being used and decide how to change the feature based on what they've found.