Murdoch & Tuning

No I don't think it was explained. He was just the 1st human they encountered who could do it.

It is explained...sort of. There are three lines of dialogue (I believe the last of these is only in the Director's Cut, not sure) where Murdoch's possession of these abilities is touched upon. They are...

The scene where Mr. Book levitates Dr. Schreiber upside down.

The scene where Murdoch first confronts Schreiber, telekinetically hurling him across the street.

The scene where Murdoch initially awakens after being captured by Mr. Hand, finding himself strapped to the chamber's experimentation bed.

All three scenes identify Murdoch's abilities as the result of evolution. He has adapted to repeat influences in his environment. Schreiber states during the canal scene that John has had, "dozens of lives before this one," indicating the city has been used by the Strangers for at least a decent length of time (months or longer, most likely).

There are ways to influence the speed at which evolution occurs, although it never happens even remotely at the speed Murdoch appears to have changed. I guess Proyas is using a literal event to convey an idea --- that evolution is the result of a changing environment, & since Murdoch's environment (& brain) change constantly, his evolution is dramatically sped up.

Scientifically plausible? Probably not, but in a lyrical context, it can be made sense of.