His statement isn't necessarily true or false (and might be both). Your assertions are however misleading.
Performance has shades of grey and can be subjective. The cell processor is potentially must faster (note the potentially) if the SPEs are used to good effect. With 3 symmetric cores on the 360 vs the cell processors single full core if someone doesn't put in the extra effort (for a smaller market) the PS3 version of a game will lag behind the 360 version.
Performance isn't always about the speed of the bare metal it's also about what you do with it. There are games where the PS3 version is well optimised and performs better (especially in first party titles) however there a lots of games where the opposite is true.
It's disingenuous to say that a first party PS3 title can't run well on an 360, it's a first party title so it will never be available on a 360. You can't make comparisons by hand waving and saying something isn't fast enough to handle something when it's never going to be available on that platform. Next you know we'll have someone saying that the PS3 isn't good enough to run Halo 3 (never mind the fact that it can't run it as it's never going to be available for it).
Disclaimer: I own both consoles - I do prefer the 360 gameplay over the PS3 however.