Even if they claimed that, it seems highly doubtful based on their results here. There is nothing in the specs that suggests that the gap in performance on a multiplat should be in favor of the PS5, the latest stats have the Series X beating the PS5 in just about every on-paper metric, CPU speed, RAM speed, bus width, pixels per second, texels per second, triangles per second, rays per second. At the very least Series X and PS5 should have near identical performance. The only thing that can explain a performance gap like we're seeing on these launch games is simply bad optimization on Series X, and the best explanation for poor optimization, on games like AC and Dirt 5, which Microsoft had the marketing rights on, is that dev kits and dev tools released too late for developers to optimize properly ahead of release.
Well saying 'nothing' isn't really accurate. PS5 has a higher clock speed for the GPU while SX has more CU's instead. If a game takes full advantage of both, then you'd expect an advantage for SX. But if a game makes use of fewer CU's, then it would be in favor of PS5.
There are some other noteworthy differences between them, like dedicated DMA controller and decompression chip, and the SSD controller is designed to offload large assets like a super fast RAM.
So depending on how games are designed, can't rule out that SX and PS5 may go back and forth on different categories. But I think overall I'd expect SX to generally be ahead by a bit for the most part. The differences shouldn't be as big as we're seeing with Dirt though.
Perhaps they're using the profile of Xbox One or something. Would like to see what it looks like on the old consoles for comparison.