Why is Eurydice mistaken as a Lynkestian?

Eurydice is often mistaken for a Lynkestian, perhaps due to the royal connections of both her parents. Her father, Sirras, was the son-in-law of King Arrhabaeus of Lynkestis, while her mother was the biological daughter of Arrhabaeus. This makes Eurydice partly Lynkestian, even though her father was not Biologically a Lynkestian but was an Illyrian since she was called so by many different authors.(Src)

And Sirrhas' father was probably the Illyrian chieftain Grabos.