Howard briefly suggests to shove Ego's seed down the garbage disposal, which is exactly what his son Tony suggests to do with the Time Stone in Avengers: Infinity War (2018).
Quill absorbs the seed Ego put on Earth; ensuring he retains some Celestial powers even after his father is gone.
Fury and Coulson being absent makes sense, they didn't become SHIELD agents until the early 1990s.
What caused the change: Yondu didn't have a change of heart and gave Quill to Ego.
The funhouse entrance looks eerily similar to the Joker's face