What if Strange did put things in motion? I've read several theories about how Strange could have went to the past/future to start things.
One theory suggested that Strange saw that Captain Marvel was the key to defeating Thanos. They suggested that Strange went back in time to the 90's and told Nick Fury that she was the key to saving the world. Obviously Strange wouldn't tell him when this was going to happen. Probably along the lines of when people start turning to ash, call her. This could very well be why she's been in hiding for over 20 years and why Fury called her in this instance. Why didn't he call her for the Battle of NY?
I wouldn't be surprised if this was an after credits scene for Captain Marvel. It takes place in the past....but it's meaning is for the future. Could set up her arrival in Avengers 4 very nicely.
Also, with Strange visiting the past, it could put some light on this scene in Captain America: The Winter Soldier.
[YT]D59g7kqH_n4[/YT]
I'm sure SHIELD would have kept tabs on Strange because of his sudden appearance, even though at that time he wasn't the Sorcerer Supreme