By "other forms of testing" do you mean something like integration testing or do you mean manually checking things?
If you run their code and within 10-30 seconds of looking at the result you can spot something wrong with it, then besides being poor coders, they're also poor testers. Since presumably the result that you're looking for is what they should be testing.
A while back I worked on a web app with developers who used TDD exclusively. In the entire time they worked there they never viewed the web app locally, but they had complete confidence in their changes and almost never broke anything. It was a bit extreme, but it worked for them and they were very effective.
By other forms of testing I mean ALL other forms of testing. People sometimes fall into traps of thinking that their favourite form of testing is better than all the others, and so they neglect the others. I'm not talking about throwing out automated tests (for instance), they are great for doing regression testing amongst other things. But to only have your automated tests and nothing else seems like folly to me.
I take the point about them being poor coders and testers, though one of them was very highly regarded as a programmer (he presented well). The thing with testing is that you cannot predict everything in advance. Even with full code coverage you cannot cover every path through the code, and as soon as your code escapes into userland all sorts of whacky interactions can take place. The last, and best defence is to actually run the code and see what it does. your eye will pick up problems you never would have otherwise predicted.
With respect to the excellence of your TDD colleagues, perhaps they would have never broken it if they had less overwhelming confidence and more "well, it doesn't hurt to check"? That minor nitpick aside, I congratulate them. I think as programmers we should aspire/strive to be better than average, to be good at our art, and it sounds like they found a way that worked for them and fulfilled that goal.
If you run their code and within 10-30 seconds of looking at the result you can spot something wrong with it, then besides being poor coders, they're also poor testers. Since presumably the result that you're looking for is what they should be testing.
A while back I worked on a web app with developers who used TDD exclusively. In the entire time they worked there they never viewed the web app locally, but they had complete confidence in their changes and almost never broke anything. It was a bit extreme, but it worked for them and they were very effective.