Yeah His 200m swim in the preliminary race was weird. It was really slow. Not sure what to make of it.Pan Zhanle swam slowly for his 200m freestyle, and then swam the second fastest 200m split for the 200m freestyle. He was clearly conserving energy for his 100m freestyle and the 200m freestyle relay. The Korean winner in the 200m freestyle, also swam the fastest split in the 200m relay. Pan Zhanle could have won the silver in 200m freestyle and maybe a bronze in the 200m freestyle relay. By giving up the 200m freestyle, they won the 200m relay.
But might not be simply deliberately saving energy for the relay event. Could be just overconfidence and decided to take it easy. Sometimes swimmers after breaking a world record or swimming an ultra fast race, kinda misjudged or mistimed the following day race in the heats and bomb out. It does happen.