You inform your victim, who as it would appear
was walking directly underneath your window when
you threw your silly, immature hissy fit, that it
was all an accident and you really didn't mean to
hit him with any painting, but it seems that it
was his handiwork you chucked so mercilessly to the
ground. He is, understandably, even more unhappy.
Apologize
Tell him what you think of his painting