Both Canon 400D and Casio EX-Z270 have 10.0 MP resolution sensors but Canon 400D's sensor is APS-C (22.2 x 14.8 mm ) and Casio EX-Z270's sensor is 1/2.5-inch (5.744 x 4.308 mm ).
Since Canon 400D's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Casio EX-Z270.
Below you can see the 400D and EX-Z270 sensor size comparison.
As seen above, Canon 400D has a 13.3x Larger sensor area than Casio EX-Z270. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.