Maybe I'm being slow: I don't understand what explanation you refer to. You give arguments for why each of the groups involved in the IPO either had no motive, or no power, to over-price the stock; but I don't see where you give an alternate explanation. I suspect an underestimated inferential distance; can you clarify?
It's mostly in the first section of the linked article. In brief, business insiders (Zuckerberg et al) get paid the IPO price for their shares. Any increase from that price accrues to whoever bought first.
In recent history, that was investment banker insiders, not business insiders (ignoring for a moment the retained holdings of the business insiders). That windfall is practically the definition of positional rent since it exists only because the I-bankers are the conduits between private companies and the public market. Remember that the I-bankers were ...
Facebook IPO'd at a price of 38 dollars a share, which apparently gave it a price-to-earnings ratio in the range of 100 - extremely, fantastically high. The price dropped pretty rapidly and is currently somewhere around 20 dollars; which still, presumably, gives it a very high P/E ratio somewhere in the forties. Now, suppose it had IPO'd at a more historically-reasonable P/E of, say, 20 - still high, but not stratospheric. That would put the initial share price somewhere around 10 or 12 dollars. Is there any strong reason to believe that the price would then have *risen* to where it is now? It is not obvious to me that the current price is supported by anything but the historical price - in other words, it's trading around 20 because it has recently traded around 25.
My point: I can't help but wonder if someone connected to the IPO had read Kahneman on anchoring. Somebody, clearly, was buying the stock at 33, just as someone is still buying at 20; I wonder if the chain of thought had that apparently-arbitrary number "38" in it somewhere, making 33 look cheap - fundamentals be damned! And if this happened, who benefited, and what ought we to conclude about the efficiency of markets?