Doesn't that description basically presuppose that you already understand compression? "HHHHHHHHHH" is 10 characters, but "10 tosses, all heads" is 21. Already understanding compression, I of course know that the second part could be efficient if encoded properly, but someone actually needing the explanation probably wouldn't know that.

It's not really wrong, and not really an "oversimplification" as the parent article calls it. It's just a bad example, and it seems confused about the audience it's trying to reach. Either they already understand compression, and it's superfluous, or they don't and it's just confusing.