Here's why:

* Boron (B) is a metalloid, meaning it has properties of both metals and non-metals. However, in this case, it behaves more like a non-metal.

* Oxygen (O) is a non-metal.

* Oxides are compounds formed between oxygen and another element.

Since both boron and oxygen are considered non-metals, the compound B2O3 is classified as a non-metal oxide.