Nonsense. Self-knowledge and introspection is a valid "way of knowing" that doesn't fall under the category of science in any meaningful way (introspection is essentially the opposite of observable empirical evidence). I also think its possible to encode or express truths about human experience in literature/poetry/art that isn't possible via the scientific method. Its also not clear that know-how (as opposed to know-that) is necessarily scientific.

That said, the accusation of "scientism" is almost always overblown and misapplied, and science certainly is our best and most reliable way of understanding the physical world. But it does have limitations, just like any other human intellectual activity, and there are methods of acquiring certain types of knowledge in areas where scientific methodology is less successful or even impossible.