Yes, in that way. Scientists can't say something is true for sure. You can argue (correctly) that gravity has more evidence backing it up. It's the accepted theory that gravity works the way it does because it lines up with every observation made involving it.

In the same exact way, psylocybin being produced by mushrooms to deter predators (certain insects in particular) comports with every observation made about it and explained with the same theories of evolution that lead to similar results with organisms producing chemicals all over the animal kingdom. Like gravity, it's bad science to say it like an absolute fact, but it's likely based on all available data.