How does EMI flux disruption differ from string flux disruption?

[Mike Sulzer]

Each coil is an antenna, picks up EMI signals.
If you wind them in opposite directions,
they generate out-of-phase signals.

Let's not try to make this too general. It is not true that EMI interference in general cancels. This only works for magnetic fields, that is, situations in which the law of magnetic induction, derived from two terms in Maxwell's equations, applies.

The humbucker was designed to cancel magnetic fields. Electric fields can kept out with metallic shields if necessary.