The definitions of “Celt” and “German”—and, indeed, practically any ethnic moniker—have changed over time. To the Romans, those who lived west of the Rhine were Celts and those who lived east of the Rhine were Germans (To the Greeks precedent, the term “Keltoi” meant something slightly different). Now, we usually think of those appellations in terms of linguistics. Celts were those who spoke Celtic languages. Germans were those who spoke Germanic languages. (For another example, in some usages, the term “Celt” was interchangeable with “Gaul” or “Gael.” In some usages, they aren’t, with Gaels forming a subset of Celts.) Now, of course, Germanic and Celtic languages are both part of the Indo-European language family, but they form distinct subgroups within that family. It’s very difficult to judge to what extent bloodlines co-incided with language, and it seems that the more we learn about history, the less concrete the concept of ethnicity in terms of blood lineage becomes. Anyway, it’s really difficult to address this issue without knowing your terms. Yes, the Celts were a people in the sense of having a shared linguistic heritage that was separate from other branches of the Indo-European language family (Germanic, Romance, Greek, Slavic, etc.). And, yes (I believe), the Celts were a people in that they to a large extent shared cultural characteristics, such as the Druidic religion.