Theres 3 garre Dialects. Your correct about one of them. the first dialect is af garre koofar which is garre spoken in its purest form. Then you have afan garre which is borana with a somali accent and some somali words. The last dialect is af garre maleel which is af garre with maay maay.That’s because the language the Garre speak is Afaan Oromo in the Borana dialect with a slight accent.
When it come to language, all eastern dialects are closest to Somali in language, but the sound. I personally think it could be Hararghe or Borana. The 2 are really similar in accent but dialect differs a bit. Boran is closer to old and original Afan Oromo.
We speak in different dialects cause of us living in different places.