Harry will be angry at both of them, but probably more angry at Daphne. However, since Draco is going to be sullenly prideful, not explain much at first, and refuse to stop "dating" Daphne, Harry will be irritated at him, too.

He can feel irritation. What he doesn't feel is rage.

Harry just thinks about Draco's artistry as something he admires about Draco. He doesn't automatically think that Draco will look for something similar in his partner. In fact, he probably thinks that Draco will enjoy being the calm one in the pairing, so he can throw drama fits and Harry can take care of him.

Ginny explains her motivations in the next chapter.