You have completely missed the point - there is no such thing as plagiarism in the visual arts. One cannot copy and paste a painting like one might copy and paste a passage of text. It’s no more possible for a painting to be an exact copy of a paper collage than it is for a singer to exactly reproduce another’s song.
When you listen to Jimi Hendrix’s version of “All Along the Watchtower” you’re not hearing Hendrix plagiarize Bob Dylan, you’re hearing a separate interpretation of the song; one that expands the original and connects the two artists. This is what is happening when you compare the painting by Thomas with Matisse’s collage - nothing more, nothing less.
I disagree. Visual arts are different from performing arts, because in performing arts, there is a clear division between the work and the performance. With visual arts, there isn’t.
When Hendrix plays a Dylan song, Dylan is acknowledged and understood by all as the songwriter. When one artist copies the work of another (and that’s exactly what this is: copying) without a clear credit to the source, then it is the equivalent of plagiarism. in fact, artists own copyrights in their works, and thus this is an instance of copyright infringement. We’d have to research the complicated issue of the dates involved, but as a rule, that painting is illegal, and the Matisse owners have the right to have it destroyed.