When applied to "people" in the plural, I think of a huge crowd, milling around, possibly "churning." I don't think it speaks to the "mood" of the crowd. I may be wrong.
When applied to an individual, it clearly denotes anger - boiling mad.
It probably refers to a large mass of people rushing or pushing to and fro in a state of agitated or confused motion. This may be a literal or figurative motion.
Alternatively, it may simply mean that the people are extremely angry.