English is a hybrid of the Germanic and Latin language groups. It has a simplified Germanic grammar and basic vocabulary of common words, but the majority of the vocabulary comes from Latin languages.
58% is Romanic, but big part of it is not a 'common tongue', but scientific/military/political vicabularies. For example, numerical system of British sheep-breeders is still Cumbrian (Celtic one).
And yes, grammar have the strong Celtic influence - 'Do' in question and negatives, system of 'continuouse tenses' and so on.
The problem with his argument is that English has diverged much further from its language relatives than someone from another European language group might suspect based on his experiences with his own native language and its relatives.
I happened to be talking to a student of linguistics during Easter, and she agreed that of the major European languages English is probably the most irregular and inconsistent.
Knowing English does not help you with learning German in the same way that knowing Italian would help you with Spanish.