Fredrik is a football journo at the second largest newspaper in Norway.
Albeit Norwegian journos are not likely to be breaking any big news for players/clubs from outside of the Nordics, but he clearly has contacts at United that will dripfeed him certain info. He's one of the Norwegians journos that has the best relationship with Ole (certain outlets have clashed with him), and I think they have common friends between them that convey certain info, like him posting leaked lineups pretty often ever since Ole became the manager.
But he's also clearly a massive United fan. He doesn't do his reporting via tweets normally. A video journalist mostly. If he tweets reactions to others info/tweets I wouldn't take it as him knowing something more about it, just that he's as gassed as the rest of us about potential transfers and whatnot. But if he does tweet specific info I would consider it extremely likely to be true. He hasn't been bullshitting anything or attempting any guesses so far.