Yes, the case you mentioned would also qualify as a double check.
But it also depends on what your definitions are. If the Perft result does consider that to not be a double check, it doesn't mean you have to abide by it.
Yes, a double check is when two pieces give check at the same time. It doesn't matter how you got to that position. As to whether there's an error on that wiki, it's probably best to try to ask its author. Maybe they can provide the full list of positions for you to compare.
I can think of two ways of giving double check while promoting. One is where you ...