Trending OI Sentiment is nothing but the difference between the Chg. in Put OI & Chg. in Call OI (Put OI minus Call OI) for the specific strikes at specific time intervals.
If Call OI is significantly greater than Put OI, it suggests a more Bearish sentiment.
If Put OI is considerably higher than Call OI, it suggests a more Bullish sentiment.
Option sellers are big institutions, option buyers are small. Big guys are usually right. A build-up in Calls usually means big people are selling Calls, and are betting the market won't go up. A build-up in Puts means big people are selling Puts, and are betting the market won't go down. So a strike with a huge call OI will be resistance, and a strike with a huge Put OI will be support.