That would be it.

One of the other things, that I haven't seen discussed much but seems to be going on, is that TCDS works by altering local ion concentrations. But those ions have to come from somewhere- and so it may be that TCDS lowers action potentials in one part of your brain but raises them elsewhere. (Brains are big, though, and so it seems plausible the effects elsewhere would be tiny. Ions would also be small enough to cross the blood-brain barrier, so many they just get pulled out of your bloodstream? It's times like this that I wish I had taken more biology.)

After watching the video, though, I'm much less pessimistic about electrode placement (or size- it looks like ours were reasonable).

Impaired learning, IIRC - one study I read about recently mentioned that when the setup was reversed on the head, learning was not enhanced compared to baseline but damaged.

What effect could misplacing the electrodes have besides stimulating a different part of the brain?

Nausea and apparent bright flashes of light. ie. What it looks and feels like to stimulate certain different parts of your brain. From what I understand this isn't a particularly big deal, just unpleasant.