What counts as a segment is the flight number. One segment = One flight number. So, CMN-TLV counts as 2 segments, becase there is a connection in Barcelona, and therefore a change of flight number. For the same reason CMN-TLV counts as 2 segments for the total count of 20 and also 2 segments for the continent limit of 4.

On the subject of surface sectors, they do not count towards the continent limit, but they do count towards the 20 limit. Any surface sector, even those between same-city ariports, count as segments.