In the Dads Army Theme/Signature tune why is Mr Brownlow mentioned when he is not in the series?

Question

Why is this seems strange

Answer 1

Have no clue honey.

Answer 2

The signature tune is a World War 2 song from that era - not specially made for the series. It is referring to the Home Guard.
the words are :
Mr Brown goes off to town on the 8.21
He comes home each evening and he's
ready with his gun .... so,
Who do you think you are kidding Mr Hitler
When you think old England's done

(this is referring to the 8.21 train)