Well I think there are two things here. Yes, they had black hole experts work on the film and even generate the film's blackhole images (iirc) from Kip Thorne plugging in relativistic formulas into Mathematica. That is probably what your friends are referring to. Of course, any Hollywood science fiction movie also has some make believe in it. In this case the inside of the blackhole allowing him to communicate with his daughter and therefore save himself didn't make a ton of sense (I would assume paradox, but I think the laws of physics break down in the singularity so they used some extremely heavy hand waving). That part isn't what your friends are likely referring to.

I thought the music, acting, and triumph of humanity were pretty inspiring much like Star Trek can be despite the fact that most of the technology violates the laws of physics. You may have thought it was a terrible movie which is fine. I thought Star Wars Rogue One was one of the most boring films I've seen in the last decade, but a LOT of people loved that film.