I half-agree with the GP, that he shouldn't be above the law just because he was PM, but also, the purpose of detaining and questioning people for entry is to determine whether they pose a risk (even though I think that's dumb). A former PM is probably very low on that list.
It should be enough when they found that I have a
diplomatic passport, [that I’m a] former prime minister.
“It should be enough when they found that I have a diplomatic passport, [that I’m a] former prime minister. That should be enough for them to understand that I don’t represent any problem or threat to this country and [to] let me go immediately, but they didn’t.”
And:
“I was surprised, and I was provoked,” he said. “What will the reputation of the US be if this happens not only to me, but also to other international leaders?”
So he doesn't really care about the "brown person" paranoia, all he cares about is "diplomats shouldn't be treated like Arabs", which I personally find distasteful.
He had a diplomatic passport.
[0]: https://en.wikipedia.org/wiki/Passport#Diplomatic_passport