This is true only for erasure RS-codes, but not for general RS-codes. In erasure RS-codes you must specify which points are corrupted and the decoder discards them.

For general RS-codes you don't need to detect which points are corrupted. An intuitive explanation of the decoding process here is that, if a small number of evaluation points are corrupted, then the original degree n polynomial is still the closest polynomial to the (slightly corrupted) set of evaluation points. The decoding algorithm uses this fact.

This however comes at cost. General RS-codes can correct only half as many errors as Erasure RS-codes.