The first event in a particle flow is always a global event, whose contents affect all particles in the flow; the rest are local events. Although a global event has the same name as the Particle Flow source icon, selecting the source icon in a viewport doesn't highlight the global event, nor does highlighting a global event select the corresponding source icon.
Global event (highlighted)
By default, the global event contains a single Render operator that specifies rendering properties for all particles in the flow. You can add other operators here to have them act globally, such as Material, Display, and Speed.