The men Paul met in Ephesus were apparently members of just such a sect. For it seems that after John’s death, syncretizing unitarians had themselves started initiating people “into John’s baptism.” By this, they probably meant they were purporting to initiate ‘in the name of John’ or perhaps even ‘into the name of John’ — neither of which John himself would ever have done.
Clearly, this ‘Spirit-less’ rite was certainly not the Christian baptism John himself had administered. For even while baptizing with water, John had urged his baptizees soon thereafter to become the disciples of the Spirit-baptizing One — Jesus Himself. Indeed, John’s disciples were never even supposed to be ‘rebaptized’ — neither by Jesus, nor by anyone else.