> Companies never have a negative price. Also, just look at stock graphs. Companies are not priced by geometric browning methods.

Geometric Brownian motion can't take negative values either, so I don't know what you think this proves. While it's true that stock prices don't literally follow geometric Brownian motions (+drift), you can't tell the difference from stock graphs. (You can tell the difference with statistical tests if you know what to look for, e.g. volatility clustering, but humans can't tell by eye, and naive classification ML models will not perform well.)