On gradient boosting and types of encodings

I am having a look at this material and I have found the following statement:

For this class of models [Gradient Boosting Machine algorithms] […] it is both safe and significantly
more computationally efficient use an arbitrary integer encoding [also known as Numeric Encoding] for
the categorical variable even if the ordering is arbitrary [instead of
One-Hot encoding].

Do you know some references that support this statement? I get that Numeric Encoding is more computationally efficient than One-Hot Encoding, but I would like to know more about their supposed equivalence to encode unordered categorical variables in Gradient Boosting Methods.