You think so? Rachael thought it happened on Thursday morning, the one day she should have remembered what happened. Jane, Kate and Russell say Thursday was the other group when the guy was videoing. Matt and Rachael had a tennis lesson every day from 11-12 noon. Rachael usually arrived early for this, but she never mentioned the video incident just before her lesson on Thursday. Jane thought Rachael was in the daily classes at 9-9.15am with Kate and herself but she wasn't. Dianne says she was in that class, but no-one mentioned her at all.
It's not 'sinister' at all, just an example of what terrible memories some of them had.
Nothing to do with 'terrible memories' IMO - although I agree that different people do have differing levels of the power of recall and different perceptions of time and distance.
Why would anyone expect them to remember precisely how every minute of every day of that week had been spent - and not only to remember what
they did and said - but what 8 other people did and said too - when they had absolutely no way of knowing what was going to happen - and so had no reason to make a concerted effort to carefully commit stuff (which was unremarkable at the time) to their memories for future reference.
Can anyone precisely recall every tiny detail of how they spent every minute of the last 5 days, including the exact time they did each and every different little thing - as they went through the days, - and remember exactly who said what to whom and when?
Taking photos was just one tiny thing amongst all the other things they did that day. The fact that they didn't all have identical memories of what happened re that - or anything else for that matter - is perfectly normal. Ask any policeman.