[jdmichal]

It's a slightly different place of articulation. The Arabic <ع> is pharyngeal, while the "R" you are thinking of is uvular.

https://en.wikipedia.org/wiki/Pharyngeal_consonant

https://en.wikipedia.org/wiki/Uvular_consonant

https://en.wikipedia.org/wiki/Place_of_articulation#/media/F... (9 vs 10)