I think your missing the point of the post. This had nothing to do with total volume today. It had everything to do with opening orders in the May SPX options. There were between 5,000 and 13,000 lots of essentially market orders to buy of out of the money puts. I haven't seen this size of opening orders before as long as I can remember. This has a huge effect on the settlement price of the VIX and creates opportunity for customers to participate in the SPX opening process. The news stories spin this as VIX manipulation, but I don't think that's the case. The CBOE is very transparent on how the VIX is marked (based on the opening price of these SPX options). Anyone who thinks the price is too high, is free to sell them.
It was a great catch and a great opportunity to make quick money on a day trade. Maybe next time you should not share.
Not in SPX on VIX expiration... you need to understand the dynamics. On VIX expiration date, some traders who are long VIX in the derivatives that are expiring want to push the VIX higher. VIX expiry level is determined with the opening of SPX options. So usually VIX is 'manipulated' done by massively bidding up far OTM (puts) in the next SPX options... since the IV jump from a 5 cents options to a 30 cents one is a lot... so that's very effective. Cost of doing this is limited... well... limited it will add up But if you're long a few thousand VIX April futures, and long the 16 strike ... boom... It's also possible that two or more parties collude... one bids up those puts and another one sells them, then the next day or asap they reverse the trade OTC. That would be illegal though, since it's market manipulation... but it's hard to track the OTC trade I guess...