It's probably not short selling; IPOs are more difficult to short than its probably worth to try.
The short comes from hedging a long IPO with an option position. For the typical retail investor, this means selling covered calls on a long position, and then waiting for some more-optimistic douche to exercise them when the price is already far enough in the money for the seller that the seller is gonna clear a profit anyway.
It's a parasitic strategy, meant to take advantage of those who are even more clueless than the jewish clever-asses who think they're going to mAKe A kILlING with an option hedge like that