To be fair to the OP, they saw the words "First Class" and didn't realize that on a domestic flight here in the US, all that means is a wider seat with more legroom, free booze and generally some food service. Food that is about what economy passengers used to get here on domestic flights many years ago before economy meals were scaled back and eliminated.

The people not in First Class on the OP's MIA-JFK flight received an experience not terribly unlike that found on RyanAir or EasyJet. The OP should be thankful they didn't have to endure that.

Our common language is English, but a lot of our words mean different things. Here in the US, domestic First Class ain't anything special, but it sure beats being in the back of the bus.

Connect at JFK in February when there are nonstops between Miami and London? Yikes.