A few night ago(August 2019, Nassau Bay, TX), I saw a hummingbird feeding on a spider lily under a streetlight at night.
What an interesting experience!
The Hummingbird was probably on route south. There is no hard evidence that Hummingbirds don't migrate at night, so it was very possible that the bird you saw had just finished or was embarking on another leg of its journey.
They must feed often while migrating to keep up their energy levels.