Which engines are we talking about?
The Trents or the Ge90's? (on the photo)
Cowling or fan diameter?
Anyways, it's not totally true, the fuselage of the 737 is larger in diameter than the fan of the Ge90's.
Regarding the cowling, that's a little more interesting, but I believe the 737 fuselage is wider by just some inches in fact ???