Applying Occam's Razor, the simpler explanation is that PG actually does use nickb as a sock puppet, made a mistake, and then attempted to cover it up using April Fool's Day as a convenient excuse.
it must be a joke. i looked back at nickb's posts and he mentioned depending on textmate?! no way a vi user would betray the brotherhood, even in puppet form.
The chance that the mistake would happen today in particular is what makes it not the simplest explanation. That also wouldn't explain why the comment would appear on pg's comments thread.