I would like to understand what is happening, the value of ravencoin is rising and the change in Bitcoin is falling. why this difference

Bitcoin had a nice pump and RVN was already going parabolic against bitcoin. You can't expect it to rise forever. RVN/BTC and RVN/USD are different pairs. RVN/USD is going up because BTC/USD is going up but RVN/BTC is going down because people took their BTC profits when it was 1600 sats.
It can still rise against BTC though. All you need is more buyers than sellers.