No, I did not mean to contradict what you said. I was referring to some people who misunderstand the name to be associated with Hindus in the religious sense, especially on this forum. Basically being Hindu is a geographic affiliation and not a religious one. I knew that this was a corruption of the term Indus or Sindhu, just not sure who did it - Arabs, Persians or British as you stated.
I did not mean that its antiquity is of any relevance, just to make a point to people that why the term Hindu could have no reference to the religion.
Well the variants are apparently since the time of the early Persian/Aryan contacts. The early Arabs would have used what they would have learned from the Persians. The British obviously learnt the same terminology.
The ting with the British rule was the differentiation between Hindus as a religious group rather than a geographical group. The first census they did was in 1961 using these terms under religious affiliations. Prior to that no one knew the exact religious compositions of different areas.
Infact, many Hindu scholars also prefer to use the word Vedantists or Sanatan Dharmi to describe their faith rather than Hinduism. And Vedas are of course one of the oldest that according to many people fall into the category of revealed books