Both Olympus TG-4 and Fujifilm XP70 have 16.0 MP resolution sensors but Olympus TG-4's sensor is (1/2. ) and Fujifilm XP70's sensor is 1/2.3-inch (6.17 x 4.55 mm ).
Since Fujifilm XP70'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 Olympus TG-4.
Below you can see the TG-4 and XP70 sensor size comparison.
As seen above, Fujifilm XP70 has a infx Larger sensor area than Olympus TG-4. 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.