They had about 3-4 samples from this group in particular, and it was J-L283, and the group being connected to those J-L283 dominated along the Adriatic and the R-L2 dominated in the Alpine-Middle Danubian sphere. So its a clar link, fused group, which was already evident from their archaeological characteristics which points towards a fusion of various influences and Illyrian as well as Upper-Middle Danubian/TC/R-L2 connections.
The connection goes also to Italy and ther Upper Danube the same time for those key cultures for J-L283 (Cetina, Istrian hillfort culture and Posusje).
Actually, J-L283 might have been coming with Yamnaya to Europe, as one of the few other lineages - but that's debatable. In any case, by the EBA-MBA, the time frame we're primarily talking about, they were IE, because we have a continuous development from the mentioned three Adriatic groups (some question Cetina, but I stll mention it as a candidate) into the Illyrian sphere. Istrian hillfort culture and Posusje got pressured and influenced by the Tumulus culture the same time, this created the Proto-Illyrians probably.