Yeah, different things. Electrochemistry involves motion of charge carriers through some kind of medium, and can happen over very large distances even if the medium is just the polymer surface of the board. And needless to say it doesn't care about junction angle at all.

"Electromigration" is the motion of individual conductor nuclei out of the wire due to scattering with electron momentum. Effectively, when electrons are asked (by the electric field in the conductor) to make ultra-sharp turns at nanometer scales, they sometimes collide with the aluminum/copper/tungsten/whatever nucleus instead, knocking that nucleus away from where it should be in the crystal. Over time, this erodes the junction, increasing electrical resistance, and eventually the chip starts to fail at voltages and clock rates it used to handle well.