This is because the instrument is simulating the characteristics of an acoustic piano. The digital pianos in Roland’s product lineup are designed to make the higher notes from G6 upwards sustain naturally, even when you don’t press the damper pedal.
In an acoustic piano, a part called the “damper” is used to physically control the vibrations of the strings. However, since the piano strings are shorter as you go up the scale and the notes die out more quickly, a damper is not used on these higher notes.