There's no other reason for Raiola to be there other than to discuss a move. Unless its a contract extension, but very unlikely considering we've not heard anything.
I know Pogba and him are good friends, but not such good friends that they'll be on holiday together. Di Marzio had said last week that Raiola will be flying to Miami to meet Pogba, and turns out he was right. So it obviously has to be a transfer, the only question is if its to Manchester or Madrid.
No other reason that his agent will be in Miami.