To begin with, it is a singularity, that’s explicitly confirmed through multiple easter eggs in the series.
There's also another easter egg outside the show itself, included in official merchandise. When you purchase a JCJenson pen, you receive a note addressed to Cooper9 scientists. It explains how to survive various catastrophes, and one of the events listed is a "singularity event"
So, why doesn’t the Null behave exactly like a black hole?Simple: it’s not exactly a black hole. It’s more like a Big Crunch, as implied in the ester egg, a point where the laws of the universe collapse in on themselves.
That’s why there’s no gravitational pull around the Null. However, black holes and big crunches follow the same physics in terms of mass and density, so the math still checks out when doing calculations based on their size and gravitational characteristics.
So yes, the calculation is still correct, but if we want to nitpick, yes, it won't suck everything in like a black hole, but it will create a local collapse, which is not instantaneous throughout the entire solar system. The result is the same, and the calculation proves it. In my opinion, when they use the term “black hole” is mainly a simplification, not a literal black hole.
First of all, the gravitational waves reference isn't even a statement, it's an easter egg. And easter eggs are confirmed canon within the series. Because the glitch confirms the canonicity of one of the Easter eggs, and encourages people to look for the other Easter eggs, referring to them as “extra details.” So he confirms once again the canonicity of the other Easter eggs with this sentence.
Second, this line is also a textbook case of the argument from ignorance fallacy, because saying “feats > statements” is usually just a rhetorical device, not an actual argument.
Just because feats are generally seen as more reliable doesn’t automatically make a statement false. To actually claim a statement is false, you need a feat that directly contradicts it. Only then can you use “feats > statements” as a valid argument rather than a rhetorical slogan.
But that’s not what’s happening here, so the argument is fallacious.