While Samuel L. Jackson isn’t too specific, it sounds like there’s something within the character of Captain Marvel, such as what her specific powers and abilities will be, that could relate directly to how she will be able to help in Avengers 4.
Since Samuel L. Jackson will co-star in the film alongside Brie Larson as a younger Nick Fury, he’s privy to whatever the script reveals.
We know the movie will see Captain Marvel battle the Kree, and Thanos certainly had dealings with them in Guardians of the Galaxy.
Alternatively, the plot could relate more directly to the story being told in these two Avengers movies than we thought.