Following what @Kovoschiz wrote I had a look at List of bus rapid transit systems and learned there is a BRT Standard and bus rapid transit systems can be scored using this BRT standard.
That said I think the term “BRT” should be largely removed from the definition of highway=busway, it is too limiting and thereby causing confusion.
Most, or at least not all, busways are not BRT’s or “BRT certified” but on the other hand, BRT’s are always busways.