[quote=@Eddie Brock]
<Snipped quote by Burning Kitty>

Technically, we don't know that he is yet. But regardless, the director/writers have explained that he was trapped in the time loop with Dormammu for a [I]long[/I] time; long enough to achieve a fair bit of mastery.
[/quote]

He got a fair bit of mastery with time loops, no other magic was shown.