I don't think this does a very good job of explaining the HyperLogLog, honestly. A slightly less contrived example would've been useful.
And the problem posed was not to count the number of visitors, but to count the number of different people who visited... the fancy word for that is the "cardinality of unique visitors" but "number of different people" is just as accurate.
Counting the number of people could NOT be done with the same amount of space. This example required two simple counters on the blackboard... call it 30 bits of memory, assuming you didn't expect either counter to get more than 8. That's just about exactly enough space to store ONE social security number... and nowhere near enough to count the unique people.
They may not specifically use the word "distinct" (opting for phrases like "unique visitor" instead), but they certainly make the concept clear.
My concerns are not really about the contrived usage of only 2 buckets and decimal numbers. This may give a picture to start with.
But, this is a pity to elude how the final cardinal estimate is computed. And this is shame to publish a gist so sloppy : all key points are buggy (bucket assignation, count of leading zeros, final outcome).
I started my day with "Oh fine, a post witch may help me to understand quickly how hyperloglog works" but I was so confused after that reading, that I forced me to dive into the paper and a high quality code (redis implementation) to leave with a better understanding and no more false assumptions.
This may be ok to simplify an algorithm to help people to grasp it. But at least, as an author, we have to give a true insight.
:)