In Avengers: Endgame, when Dr. Banner did the snap to bring everyone back, we see Ant-Man looking outside and saying
Guys... I think it worked!
But what exactly did he see that made him say that? There were just a tree and a few birds outside.
In Avengers: Endgame, when Dr. Banner did the snap to bring everyone back, we see Ant-Man looking outside and saying
Guys... I think it worked!
But what exactly did he see that made him say that? There were just a tree and a few birds outside.
The snap affected all creatures in the universe including birds, Scott is looking at the birds and realising they have come back and so he works out that the "un-snap" has worked.
Natasha: Thanos did what he planned to do, killed half of all living creatures in the universe.
There's nothing more to it than that.
To explain this further the facility was pretty devoid of life in the previous scenes and all of a sudden after the un-snap a bunch of birds are around. Seems pretty clear that the un-snap has at least partially worked. On top of that Clint's phone has started ringing in the background before Scott speaks and he probably heard his reaction to it.
Both things combined with Scott's nature to jump the gun seem like a reasonable interpretation of the events that it did in fact work.
As I remember correctly, earlier in the movie he, or someone to him, said, that the world is too quiet without half of the birds. And it could be a reference to that.