Both Fujifilm Z900EXR and Olympus E-M10 have 16.0 MP resolution sensors but Fujifilm Z900EXR's sensor is 1/2" (6.4 x 4.8 mm ) and Olympus E-M10's sensor is Four Thirds (17.3 x 13 mm ).
Since Olympus E-M10'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 Fujifilm Z900EXR.
Below you can see the Z900EXR and E-M10 sensor size comparison.
As seen above, Olympus E-M10 has a 7.3x Larger sensor area than Fujifilm Z900EXR. 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.