as to the differences between High & Low German, you may go to www.google.com
and enter these keywords:
> If there is a difference between high German and low
> German does that mean each come from a different area?
Depends, for instance on the timeframe. But no, not necessarily - as my common sense tells me ;-)
Since the advent of compulsory education and public schools many people - even if coming from a 'Low German' area - would also speak High German. I have had extended stays in Hamburg once, a North German area on the so-called Waterkant on the North Sea where Plattdeutsch (a Low German variant) is still widely known and also spoken. These people did of course also use some kind of High German - for instance when I talked to them.
Also, consider that people are moving around quite a lot during their lives, and did so also in the past. This too would often make them 'bilingual' out of necessity.
Hope this helps