Yes, sanguine is ASSOCIATED to blood, not IS. It's just my view, so don't take it too deeply. Sanguine is associated with friendliness due to humoural theory. An excess of blood denotes a the person as 'sanguine' aka friendliness and optimism.
sanguine (ˈsæŋɡwɪn)
— adj
1. cheerful and confident; optimistic
BTW, blood could also be related to
, since blood is the fluid of life obviously.