Put $300 into world cup event contracts through a brokerage. CPA said gains file as investment income. Is that right?

Usually put a small entertainment budget toward sports betting during big tournaments. This year I did it through a brokerage that just added event contracts, put in $300, currently up $52.

Mentioned it to my CPA and she said event contracts through a regulated platform file as investment income, not gambling winnings, so it will be in different schedule, different rate depending on holding period. I assumed it would be the same as my sportsbook stuff.

Has anyone here filed prediction market gains? Is the brokerage route genuinely different from a tax standpoint or was she oversimplifying?