Not entirely unproven. He instagrams and tweets pictures of himself throwing gang signs and hanging out with known gang members on a fairly regular basis. There’s no proof he’s active, or has committed crimes, but there’s lots of proof that he’s embroiled in the culture. And after the Hernandez thing nobody with half a brain will sign him, so he’ll be a Jet or Raider.
If flashing gangs signs in a picture is an indication of anything there are millions of teenage, suburban white girls who are gangsters.