I think what you are confused about is the difference between concurrency and arrival rate.
Concurrency is how many things are going on at a snapshot in time. The Arrival rate is how many new things arrived during a window of time.
During the snapshot there were two concurrent events. The arrival rate during that entire second is 5 events, because there were 5 events that started throughout that second. The key relationship to grasp is that a large amount of concurrent connections can come from a high arrival rate and/or long lived connections (see Little's Law).