To be clear, connected flights with a plane change and flight change still is just one segment.

But, there are times that flying the same plane with same flight number can count as two segments. for example, Tampa to Rochester. If the flight has a stop in Baltimore, but you bought a single ticket from Tamps-ROC, it is one segment. If you buy TWO tickets, one from Tampa to BWI and one from BWI-ROC, then it is two segments, even though you are on the same plane/flight number.

Bottom line, plane and flight number are NOT the determining factor. It is how you bought the ticket.