It was probably a hoax. There's been a ton of hoax videos on TikTok about "hidden codes" that supposedly "unlocks hidden features" or "lets you know if your phone is hacked" with instructions on entering certain codes into the dialler in order to bring up text that most people don't understand.
None of these claims are actually true. The codes they tell you to enter are general carrier diagnostic codes and don't actually do what the TikTok videos claim. They'll bring up some diagnostic information that the general user won't understand and the videos trick people into thinking the text means something else.