If you are accepting that arabic speaking people are arab, then yes, some Omanis are black having migrated centuries ago. This is a construct of the Arab League which claims that anyone living in an arabic speaking country is arab so they can claim control as an arab state to expand their influence.
Genetically, black people are not arabs.
I don’t think arabs give a darn about our genetic terms:
The Ancient Arabs’ Description of the Pure Arabs
The best way to get a true picture of what the original Arabs of the past looked like is to ask the original Arabs of the past themselves. So let’s take a look at what the original, pure Arabs of 1400 years ago said about the appearance of the pure Arabs...
Furthermore, if you cannot imagine how a kenyan black of any tribe, with an arab father, might choose to describe himself as an arab - as he would be entitled to - for the benefit of belonging to the ruling class, there’s nothing more for me to say on the subject.