Guys guys guys .. this is neither good news nor bad news, just some eccentric guy saying something almost utterly random. Should not be taken seriously.
Anyways, the 360 should be more than *capable* of running any title that will appear on PS3, the capabilities of each unit is more than up to the task. Of course, the end result's degree of success or failure depends upon a drastic number of variables (quality of dev kit, competence of coding teams, vision of the producer, budget allotted, time allotted, internal politics, etc, etc).
Just looking at the numbers game for the hardware itself, the r500 graphics engine shouldn't be all that far off of the g70 core that the PS3 is set to use. One only has to look at the PC Market (x1800 series vs. 7800GTX) to see that they are fairly close to being equal in most respects, even if the PC card is the r520. Moving on to Cell vs. the 3-core IBM proc, the strengths and weaknesses of each are still very similar, and you can look at total die size, transistor count, projected integer and floating point performance, to determine that the class of software that each is going to be able to run should be completely in the same class.
In summary, a skilled and budgeted team could almost certainly make a version of MGS4 for x360 that would be damned close (probably too close for anyone but tech geeks or fanboys to complain about) to what is on slate for PS3. On the same token, same goes for any x360 title, you name it and it could easily be on the PS3. In fact, you will probably see a lot of instances where the 360 version is superior, and vice versa.
Bah