I hope he means germanic instead of German. Many of those 'Germans' were actually from Prussia (such as my gg-grandparents), Austria, and Bavaria and many others, which were all germanic but independent countries. Not to mention others that were germanic components in other countries such as Switzerland.
By the time Germany became an actual state, millions of 'Germans' had already made their way to the USA.
I doubt there is any standard definition, of what criteria are used for grouping. Unified modern Germany didn't exist, until the late 1800s, for example. Prior to that, it was "Bavaria," "Prussia," etc.
But there is a cultural, linguistic, identiy parameter which is useful.
At the time these groups migrated to the Americas, they thought of themselves as "Irish" for instance. Census records in America classified people, based on self-identication.
People said "Irish," "German," etc. A person from Northern Ireland, that today would call himself "Scots-Irish" would have only stated "Irish" in the 18/19th century.
So the categories in the short video are valid, for those they describe.
(In linguistics, "Germanic" languages include English, German, Swedish, Dutch to name a few.)
The DNA is very similar for Spaniards, and many Englishmen. But the culture, language, national identities are different.
