Russell muscled ahead of Max Verstappen at the start of Saturday's sprint event, but after a resumption following a safety car period, the Dutchman passed him on the run down to Turn 1.
Although that move was achieved with DRS not yet activated, Red Bull's speed on the straight when it is open has been a focus of attention for rivals all season.
"We know what the speed difference is," said Russell when asked by Autosport about Verstappen's pass.
"I think we believe we could take the rear wing fully off, and Red Bull would still be quicker than us on the straights, and that's not even a joke.
"So we don't understand what they're doing. They've clearly done something incredible... Something very, very trick.
"Kudos to them for whatever they've done to achieve this straightline performance.
"But especially with the DRS, as I said, we believe we can take the rear wing fully off and they'd still be quicker than us. So something's not adding up from our side."
Source: Autosport