usually there will be a black line showing, about two bricks above what was ground level when the house was built. It should not be rendered over as this provides a bridge for the damp to get past. If you want to hack it off buy a bolster, a club hammer, some gloves, and elastoplast.
A common source of wet walls is dripping or leaking gutters, downpipes and drains. Another source is leaking water or waste pipes which may be buried.
The render was most likely applied to hide damaged bricks. It is not very difficult to apply render that stops at the DPC.
It is informative to look under the floor, inside the house next to a damp wall.