a weird question and i don't know if anyone can answer it, but does anyone know how difficult it is getting a visa to work in the united states of america if you were born in the middle east (namely beirut, lebanon) but you hold a british passport?

i've applied to do a camp thing with BUNAC and they called me today and said that MAYBE the US immigration people won't let me in to do my thing, but seeing as i can go on a visa waiver without any worries, is this a real concern? i know i can google this and i have already asked BUNAC but i wanna know if anyone has had any experience with this or knows someone who has.