It IS from a whole group of people: the group of people who signed it. Two persons who happen to be Latino = Latinos, plural. You're supposed to distinguish between their use of a plural designating a community - African-Americans - and the use of a plural meaning "a number of Latinos". This letter is explicitly from a group of people on behalf of themselves as Latinos and on behalf of all Latinos who feel the same as them.

Props 2 the person who posted it... it was great.