George Booth Post (September 29, 1906 – March 26, 1997) was an American watercolorist and art educator. He was an important contributor of the California style watercolor movement (also known as the California School of watercolor) of the mid 1920s until the mid 1950s.
Post taught watercolor.
Although Post was an art educator, the statement does not say what style of art he taught specifically. Additionally, though Post was a contributor to the watercolor movement, the statement does not mention how he contributed. I think the system struggled with this, because there is an implication that Post did teach watercolor. However, the context does not specify this. 
( z1 teach :ARG0 ( z2 person :name ( z3 name :op "Post" ) ) :ARG1 ( z4 watercolor ) )