Per that article, I assume the trader bought options for a strike price of 2980. The index price dropped from 3120 to 3080, and the trader made profit on it. How is that possible?
Per your comment:
My understanding is that to make a profit out of selling PUT is only when the price is in-the-money.
The problem is that you understanding is incorrect. Barring a sudden change in implied volatility, a put's price will increase in value immediately if the price of the underlying drops.
Here are today's closing quotes for the Jan 17th SPY puts.
Str ........ Bid . Ask . Last
300 SPY 2.81 2.82 2.80
301 SPY 2.98 2.99 3.04
302 SPY 3.17 3.19 3.19
303 SPY 3.38 3.40 3.45
Let's pretend that these are a snapshot from during the day. If you bought the $300 put for $2.82 and the SPY immediately dropped 3 points, it would be worth $3.38 (the same as the $303 quote) for a gain of $1.16
Your reference only making money if ITM refers to whether the put has any intrinsic value at expiration.