Both Sony HX50V and Sony RX100 V have 20.0 MP resolution sensors but Sony HX50V's sensor is 1/2.3-inch (6.17 x 4.55 mm ) and Sony RX100 V's sensor is 1″ (13.2 x 8.8 mm ).
Since Sony RX100 V'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 Sony HX50V.
Below you can see the HX50V and RX100 V sensor size comparison.
As seen above, Sony RX100 V has a 4.1x Larger sensor area than Sony HX50V. 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.