Did you drop your ATM machine? 

Some people, when they see an acronym, will replace it with the words it stands for in their head. A subset of that group of people get annoyed when the sentence gets all muddled up by repeated words; in this particular case, you said 'CSAM material', which their brain read as 'child sexual abuse material material'.

It isn't a big deal, but as one of those people, I totally get the urge to point it out (I've gotten pretty good at looking past it but it's still a bit of a compulsion).

They are referring to your use of "CSAM material" in your sentence.