It's a sound; it works well in this group, with this mix. But these days, the old convention that 'proper' bass tone (in jazz) has to be muffled and muted is now only one possibility. So many permutations of the ways of playing jazz, and of course the various genres that consider themselves to be jazz continue to multiply, each with their own sonic conventions - some with double bass, some with electric. The first be-bop I heard played on a P bass was a Wes Montgomery album from the late 1950s where his brother Monk played one, and his tone wasn't far from what we're hearing in this video.
