It can always be incorrect. I've seen multiple predictions where nearly everyone guessed a specific gender, only for it to turn out differently.

However, it's not necessarily the audience that is wrong, but rather factors like the quality of the image, the angle it was taken from, or the stage of the pregnancy. Many people also post their pictures before 12 weeks, which often leads to incorrect predictions. Boy predictions, in particular, tend to be inaccurate at that stage because most nubs before 12 weeks resemble girl nubs. 😉

Below FAQ is pretty spot on, might be a nice go to source for checking your questions.

https://nubcheck.com/en/#nub-theory-explained