В чем различие?
https://laravel.com/api/5.5/Illuminate/Database/Eloquent/Model.html#method_isDirty
https://laravel.com/api/5.5/Illuminate/Database/Eloquent/Model.html#method_wasChanged
One of the nice stuff coming in 5.5 is the ability to know if a certain attribute was changed, not is dirty, but was changed and persisted.
Цитата мейнтейнера ларавеля