Exactly. And there wouldn't be anything particularly strange or unusual about it orbiting a star, as most stars are binary and orbit around another star, or, more precisely, both orbit a common center of mass. And surely it is the case that many of these systems involve a star and a brown dwarf, which, as you and the article states, is simply an object which didn't have quite enough mass to ignite and become a star itself. ie, a "failed star".
In any case, the article contains lots of good general info on the topic which serves to educate interested and curious folks who may not have known these things previously.
The fact that most of the exo-planets that have been discovered, via the far more common "star wobble" method, are these humongous giants several times the mass of our Jupiter, is not at all surprising either, since, being so massive they are the ones that would have the most noticeable gravitational effect on their host star and be detected (would tug on the host star more).
Same goes for the eclipsing binary method as well, where one large object, usually another star, moves in front of another causing that star to dim periodically. With either of these methods a planet anywhere near earth-sized would be very difficult if not impossible to detect, at least at this point with the current level of technology.
Yes, in both cases, the Doppler and the transit method, it’s best to have a large mass close to the star and its orbital plane aligned near earth’s point of view. But I think what this article is saying is that it’s “mysterious” that they found an exoplanet so close to the exoplanet-brown dwarf dividing point of 13 Jupiter masses—when there is nothing actually preventing it. The only question is if deuterium fusion is occurring. And that in itself probably has some grey areas in terms of mass. So the only mystery is, “we don’t know which way to call it”.