People have the arithmetic mean in mind, but their intuition of "average" is actually the median, or even more commonly the modus.

When somebody says "Average people are X", they usually mean "Most people I've encountered are X", which is the modus. Hell, I just did that in this exact sentence!

I like how we've totally ignored the guy's arguments due to some technicality in his post. That's Hacker News for you!

I think the colloquial meaning of average is "typical". Sometimes that's the mean and the median, and often, an hazy combination of the two.