Author here. The thing that strikes me here is how something like Reddit Math can fall for the same kinds of 'wisdom of the crowd' things we'd typically see on Facebook.

Some people like the analogy, so the the math isn't questioned. The post hits reddit's Best Of and more people vote it up. Now it's three months since the post and you'll only notice the error if you collapse the first comment, which is full of praise for the analogy. This is despite Reddit math being a self-selected crowd with a specific interest in the topic.

Note: I originally said 'nobody noticed the error' but as @tzs points out, some users did - collapse the first reply thread and you'll see them.