Traders most likely. They only sold around 10% of the shares in the IPO creating a fairly low float. Low-float stocks are prone to explosive moves which was likely what the underwriters wanted. If the stock can gain momentum and drift higher over the comings months, it will be much easier to place a larger secondary and collect the money the company needs.
Thanks - explains to me more fully why companies who IPO want a "large pop" - it's not just to please the underwriters and early investors or visibility.
