Complex sentence: Apart from the Germani, the report of Caesar seems to indicate that more of the Belgae (most of them in fact) had some Germanic ancestry and ethnicity, but this is not necessarily what defines a tribe as Belgic.
Split into simpler sentences: Apart from the Germani, the report of Caesar seems to indicate that more of the Belgae (most of them in fact) had some Germanic ancestry and ethnicity. But this is not necessarily what defines a tribe as Belgic.