So I know it's just a teaser, and I am confident the movie will explain this in a satisfactory way, but I don't buy how they showed Strange doing everything.
"Hey Doc, any chance we can change the nature of reality?"
"SURE THING BRAH!"
"Wait, maybe not EVERYTHING about..."
"SHUT UP BRAH I'M REWRITING REALITY!"
Maybe it's not really Strange? Dunno. Just seems awfully out of character for him to agree to something like that.