It was energy inflamed or caught afire in a nadi in the said region. When this happens, if one can, one should focus into the place where it occurred to determine if to spread it further or to compress it in on itself. However it is a good sign, if the you are having these flashes in other places besides in the spine and head of the subtle body. It proves that kundalini potential is in every part of the psyche not just in the spine and head of the subtle body. The focus on spinal kundalini is preliminary. As one practices, one will branch out to other regions and will be able to realize nadis and energy compression and explosions in other parts.