To conclude,

Impressionism and expressionism are two totally different things although they are related to each other in some way.
In ART everything is related to each other somehow, I don't know why, but if you want to know, go and ask Mr. Van Genk!
No just kidding, if you really want to know you could visit: https://www.quora.com/Whats-the-difference-between-expressionism-and-impressionism-art-music

Bye,

Robin