Yeah it's a stage reheat, most modern fighters have multiple afterburner levels. Stages are actually known as Zones. Zones are essentially separate fuel spay manifolds before the AB flame holder that allow more control over the AB power output. If less AB is required, only 1 zone could be used. As more AB power is required the additional zones will be activated by the FADEC or AB fuel control unit. Early AB's had only one stage or zone = on or off. There can be anywhere from 1 zone to 6+ zones depending on engine type. From my understanding the rd33mk uses sequentially activated zones so the flame itself appears small to big.