Both Leica C and Pentax H90 have 12.0 MP resolution sensors but Leica C's sensor is 1/1.7-inch (7.44 x 5.58 mm ) and Pentax H90's sensor is 1/2.3-inch (6.17 x 4.55 mm ).
Since Leica C'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 Pentax H90.
Below you can see the C and H90 sensor size comparison.
As seen above, Leica C has a 1.5x Larger sensor area than Pentax H90. 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.