I don't think it's even that, it's probably pure projection based on reports from the heaviest fights in entire war, that is last phase of Bakhmut battle, where one US mercenary reported that fresh Ukrainian reinforcements last around 4 hours. And since that part of the battle was just basically AFU sending people into cauldron while Russians surrounding the town and raining incredible amount of artillery shells on everything inside i would imagine Russian losses were much lighter. CIA just cranked it up to eleven and released it with close to zero thinking. Remember that lately their propaganda became so ridiculous that even Zaluzhny had publicly said that "Russia is not losing".