Thanks very much Blackpepper1, Falanouc and Katykicker - after years of doing surveys I usually just ignore any rejections or not suitables etc. but obviously I was rather put out with this (as stated, I do complete surveys properly).
Anyway, I did reply to the researcher stating that I thought I knew what the issue was and why I had done what I did and they have replied back to say that they understand my reasoning and they are happy for me to be paid
I know in the grand schemes of things it's really not worth it for the time I put into it but a. every penny counts and b. I know my attention slips extremely rapidly but it proves that I do pay attention to things when I need to