This one is actually true. Sanguine does mean both bloody and optimistic, for the reasons that your quote states.

Most of this information comes from Noga Arikha's Passions and Temperaments: A History of the Humours. Humoralism comes to us from the Greeks, especially Aristotle and Hippocrates. They believed that there are four basic fluids, or humors, which make up the human body: yellow bile, black bile, phlegm, and blood. Each of these humors was attached to a set of characteristics and emotions. An excess of any one humor would make you more prone to that humor's temperament. An excess of black bile, for instance, was believed to cause a melancholy disposition, while an excess of blood (the best humor to have too much of!) made you cheerful and hopeful. Humoralism persisted into the Middle Ages and early modern period. Avicenna writing about the humors in the eleventh century, and Paracelsus based some of his treatments on the theory in the sixteenth. Arikha attributes the decline of humoralism to the rise of laboratory science in the 19th century.

A note on Arikha: He's been criticized for missing some information at both ends of the book - as this review states, recent scholarship argues that the humours predate the Greeks and might actually originate with the Babylonians, and the reviewer also notes that some Islamic countries still use the theory today. Everything between the Greeks and today, however, is sound.