The most common derivation of Black-Scholes absolutely does assume a standard normal distribution. There are other models that don't (i.e., Mandelbrot tried to get people to use Levy distributions, and a lot of newer models are built around martingale theory), and traders have adopted rules-of-thumb that pull prices out of line with what BS says they should be, but it's certainly not the case that anyone who speaks of BS assuming Gaussians is lying or speaking from ignorance.