Another dumb Pebbles theory shot down.
http://movieweb.com/star-wars-rogue-one-rebels-fan-theory/
This one was pretty stupid, but far from the worst. A year ago Pebbles fans swore that Kylo Ren = Ezra.
People love to make theories.
Remember the fuss about Casian Andor being Biggs Darklighter because he had a mustache?
Although this specific theory is pretty dumb. Kallus and this guy don't look alike, don't sound alike and while Kallus is pretty obviously one of the Fulcrums, I wouldn't see him openly changing sides. What good would he be once he's out of the ISB? Plus he doesn't have sideburns and Kallus without sideburns isn't Kallus.
Seen a few Ezra = Snoke, as well. Even though Snoke is an alien.
shareAs I said, people need their theories.
But the nature of the Star Wars franchise today does encourage this, with the story being spread over several media types with different art styles and tones but all set in the same canon.
EDIT: In fact, I believe it's a way for people to "own" the story. If they dive into it headfirst and theorize about it (With or without hints), it makes them feel like they've gone beyond the act of passively watching it.
That's how you get dumb theories like Snoke = Ezra or Kallus = the guy from the RO Trailer.