I believe that open volume interest on a specific contract has to be bought
Nah, go grab it from finance.yahoo.com. Look up ^SPX and look at the options contracts.
However, in this case, the article is not about open interest.
First, an analogy. If I made the statement "The car is accelerating rapidly in the direction of the car in front, therefore it will hit the car in front of it", can you pick out the problems? You lack both position (could be a mile away from the other car), velocity (it could be a car starting from zero at a stop sign at an intersection, and about to turn to avoid the car stuck in traffic in front of it), and relative velocity (the car in front could be moving 10X the velocity and thus the accident would be either impossible or so far in the future as to be avoidable)
In this case, the article is not about a large bet anyone has made. It's not "the market is moving downward" or even "someone has bet the market is moving downward". It's not even "the options market is making it relatively more expensive than normal to make the bet that the stock market will move downward", but actually "the options market is making it relatively more expensive than normal to make the bet that the stock market will move downward relative to the normal cost to bet the stock market will move upward". It's implied volatility skew - so it's reflecting what the component of cost representing volatility would be IF you tried to do a large hedge vs the component of the cost representing volatility would be IF you did a large upward speculation.
Without additional context, it feels just as useless to me as the acceleration of one car in the example above. The "IFs" are important because it doesn't necessarily mean many people are trading at these prices.
What's crazy is the difference of the skew from normal (shown in the graph) is tiny (8% now is historical but it's basically been 6.5-7.5% since 2016... so... how abnormal is this really?). Can someone show this is more than noise? (this is a genuine question, not rhetorical). Also, the article talks nothing about which is different from normal - is the implied volatility on puts abnormally high? Or calls abnormally low?
Also, is the total amount being hedged higher or lower than normal? (is it extra buyers or less sellers?). There is significant open interest, but I don't know what "normal" is (and there's a bunch of open interest in December 2021 as well... so... understanding "normal" is important). If it's less sellers than normal, can we really classify that as "terrified" or is that "prudent in the face of the tail risk from election uncertainty"? (Note: options don't price in tail risk well)
"Playing the other side" here is a crummy individual trade if you sell puts. You make a small amount of money, at the risk of losing a large amount. It works well when averaged over hundreds of transactions (make a little every time, sometimes lose a lot is actually rather profitable, much like selling insurance), but doing it as a one-time event is a single "make a little, lose a lot" decision, which I would avoid. There may be some crazy strangle or something that can expose the skew better, but that part is beyond my knowledge base. For me, this is not something I'd know how to capture (if it's even big enough to do that)