Why are Samuel Adams' posters and Paul revere's engraving of the Boston massacre considered propaganda?

The artwork promoted a certain view on the events, which was that it was unnecessary violence. It encouraged people to see things in the way which Revere and Adams did. Using art or writing to promote one's views is considered propaganda. Because the "rebels" were supported, it was thought to be an attack on the British government. The artwork portrayed the scene to make the Americans looks like gentlemen and the soldiers look like the reveled in the violence. The artwork promoted the idea that "the British are the enemy", and therefore, it was considered propaganda for a political cause (to overthrow the British).