They didnt arrest him. Took his stuff just to be dicks. I didnt hear of them taking any of the Las Vegas Casino CEOs electronics. They have been predicting elelction outcomes for years. 
https://www.msn.com/en-us/news/politics/fbi-seizes-polymarket-ceo-s-phone-electronics-after-betting-platform-predicts-trump-win-source/ar-AA1u28WF