Strange Smells
Flight deck odors on 757s are far from unknown & have resulted in oxygen masks & a return before on BA 75s. The usual culprit is the well known engine oil in the air con system, which one 757 skipper I know, says happens almost every time they open the taps - perhaps not as badly as previous declarations of emergency.
We're getting into Aerotoxic Syndrome territory now, so maybe I risk this diverging into an argument about that, but are we sure this was electrical?