I would say that Thomas Martin is the exception that proves the rule. There are two points to be made here:
First and foremost, when an instrument is difficult to play for a beginner, it can cause them to be frustrated and ultimately to practice less or to stop playing entirely. Too small is better than too big when it comes to beginners, especially on the double bass, IMHO.
Second, when you are an experienced player, you can and should play whatever you like. I'm a relatively normal sized adult and I have no problem on my main instrument, which is the guitar, playing a wide variety of sizes. I own dreadnaughts, which are rather a "plus" size, standard full-sized instruments, and "parlor" instruments that are noticeable smaller in all regards. I love playing them all and they're all fine for me - but I am not a beginner.
In the video you show, the player cannot place the bow midway between the end of the fingerboard and the bridge when playing near the nut because the instrument is too big. This isn't a show-stopper for him, but it is definitely not what I would want for a new student.
I see this a lot in many areas of physical endeavor, e.g., athletics. People think that a program that works for a professional, full-time, very gifted athlete is how they should train themselves. This isn't to say, of course, that we shouldn't all learn from the best at what we do, but there is a big difference between "learn from" and "copy." One should not copy Thomas Martin's example when it comes to sizing a young person's first upright bass, or an adult's for that matter, either.
-S-