Its either a multiverse thing or some kind of fake out, but probably a multiverse thing. Wanda really cant resurrect her brother, so either she has subconsciously pulled this other version of him into the MCU or whatever actual villain is involved has done it for her as part of their plan.
Or theyre intentionally setting you up to think its the X-Men movie Quicksilver and it will somehow swerve that expectation because theres still four episodes and twists will still happen.
I'm... excited? Scared? Intrigued? It was a really good twist. I hope it goes somewhere good.