[swinglock]

Unless he is using more channels than 1, 6 and 11 the article is dangerously poorly written. Unlike what the article suggests, all other channels overlap and will cause actual interference! Do not configure your AP using any other 2.4 GHz channel, even if they already have other APs in range.

[hrzn]

The algorithm takes into account the interference of partially overlapping channels. In fact, it is part of the optimization procedure to minimize this overlap (globally, over all WLANs, but in a decentralized way), while still using as much of the spectrum as possible. This is a general optimization that is relevant for both 2.4G and 5G bands (or pretty much any other band that provides a finite amount of spectrum).