When Demetri tells Hawk that Moon and her girlfriend broke up weeks ago, Hawk replies "weeks? One week? Five weeks? How many weeks is weeks?" This is the exact same line Daniel says in the original movie when Ali tells him she and Johnny broke up weeks ago.
The flashback scene of Daniel smothering a blueberry pie on Johnny in their high school cafeteria is actually a deleted scene from Karate Kid. The scene in its entirety appears as a bonus feature in the 2021 Karate Kid 4K box set.
A popular debate amongst viewers of the original Karate Kid film was that William Zabka was the more athletically gifted actor, so "realistically" Johnny should have won his fight against Daniel. This gets brought up in the drunken argument between Johnny and Daniel, where Johnny mentions that, while the one kick was the deciding point of the match, had they actually had a series of 10, Johnny likely would've won 9 times out of 10. Daniel doesn't refute the point.
The image of Terry Silver in the internet article Hawk and Demetri were reading is a headshot of Thomas Ian Griffith that was used as his IMDb page as of the day the fourth season premiered.
The Johnny training montage pays tribute to Rocky IV (1985). It uses the same song, "Burning Heart" by Survivor, intermixes current training sequences with flashbacks and Johnny trains with what he finds around him. Ironically enough, allegedly Peter Cetera originally created "Glory of Love" for Rocky IV before it was rejected and became the theme to The Karate Kid Part II.