You will often find light notes at the beginning of chants, and sometimes at the beginning of phrases, indicated by points (as opposed to the long tractulus) in the Metz notation or by the addition of a "c" (celeriter) to the virga or tractulus in the St. Gall notation. The latter often leaves this out, but it still assumed. I however am not away of any paleographic evidence to support the interpretation in the posted recording. I would guess that is either the result of a long standing tradition of that particular schola, or it is an innovation of the director.

From a pedagogical standpoint, I would assert that it's nearly impossible for an ensemble to sing staccato well unless they have first mastered singing legato.