How so? TOS is hardly in the same continuity with itself, depending on the episodes
I’m assuming that what he means is that when someone watches an episode of TOS, and then watches another episode of TOS, there’s no mistake that it’s the same show. Then when said person watches an episode of TNG, they can see that its visual style is similar to TOS. Same with DS9, VOY, and to a lesser extent, ENT. Even the Abrams films have a visual style that at least tributes TOS, if not outright matches it. DSC season 1 didn’t seem to follow that pattern. If someone watched the show and didn’t know it was a Star Trek series, they might have mistaken it for a stand-alone Sci-fi series that had nothing to do with Star Trek besides ships with saucers and nacelles and transporters and aliens that are said to be Klingons but look nothing like what we’ve seen before (and the same goes for their ships.)