Yep, I think you only have to go back about 2,500 years to when German and English were the same language.
I believe that is one hypothesis, but I don’t think it’s the consensus. I would defer to one of our resident linguists on that.
I’ve not studied either German or a Scandinavia language formally, but I’ve spent quite a bit of time in Germany and in Norway, and I have to say that I found Norwegian easier to learn than German.