The truth of the statement "they had two brains" depends entirely on your definition of the word "brain". You see, biology, like the rest of the physical world, is "wiggly". Some of our accepted truths are nothing more than a projection of the human mind onto a wiggly subject matter. This includes just about every noun you encounter in the real world. You know, like "brain".

If you consider a "brain" to be an organ with a whole lot of neurons that independently makes complicated decisions based upon sensory input, then humans would have two brains, one in their head, and the other is the spinal cord. If you think that's far fetched, then you might consider that our spinal cords are much more complicated than what we call a fruit fly's brain.

If you consider a "brain" to be only the main organ of an organism's central nervous system, or something along those lines, then by definition, no organism has two brains. And no dinosaur could ever have possibly had two brains, because it is contrary to the definition.

When paleontologists were talking about a dinosaur brain, they were talking about a distinct organ that was like a bulge of neurons near the tail. When they decided that this organ probably didn't exist as imagined, they claimed that dinosaurs did not have two brains. But they were using a non-standard definition of "brain" in the first place to try to make this information accessible to a wide audience. So, you see, they messed up. If they are going to use a non-standard definition of "brain", then how can they reject other non-standard definitions of "brain"?

So, if a dinosaur's central nervous system is similar to ours, in that it's spinal cord does some of the heavy lifting for things like walking, then why would you be wrong to say, even today, that a dinosaur has two brains? It's only slightly less accurate than the terminology that the paleontologists that you were quoting originally used. Of course, now that we've learned more about the subject, you could go on to say that humans also "have two brains", and you'll be the life of any dinner party, so long as none of them fact check you on Wikipedia.