This might be how the term steganography is mostly used these days, but I disagree that it's the definition of steganography.

An early example of steganography is writing on the scalp of a person and concealing it with the regrowth of hair: https://en.wikipedia.org/wiki/Steganography#History . The message is clear-text, you just have to know where to look for it. Which is the same as in the blog post.

Some other non-computer examples: https://www.commonlounge.com/discussion/4bc16dbc2c7145ff87ad...

At the risk of "appeal to authority", my field of study is cryptography, and we used steganography in this broad sense.

tl;dr: I agree with the blog post in that it is steganography.