Both Olympus E-M10 II and Pentax K-01 have 16.0 MP resolution sensors but Olympus E-M10 II's sensor is Four Thirds (17.3 x 13 mm ) and Pentax K-01's sensor is APS-C (23.7 x 15.7 mm ).
Since Pentax K-01'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 E-M10 II.
Below you can see the E-M10 II and K-01 sensor size comparison.
As seen above, Pentax K-01 has a 1.7x Larger sensor area than Olympus E-M10 II. 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.