Not necessarily true. You can experience something and have a memory of it, but not understand its significance until you gain more information later on. I am by no means eidetic, but I do have a very freakishly strong memory, especially long term things. It does have a high correlation with high IQ (and depression as one might expect), but its not a given and there is no direct connection to having both. Most people, like you said, are no apple live in the moment mouth breathers who only actually remember things that directly impact them in the moment. Still others who are smarter compress experiences into a kind of mental short hand that reflects their interpretation at the time of the experience. Then you have people with excellent memory who basically actively have to filter shit and can recall specific conversations and observations that would seem to most to be completely irrelevant at the time. If you are a trial lawyer, your experiences with the average witness probably involves mostly the former two types. But you can have complete retard Rain Man types with perfect eidetic memory, but lack the reasoning skills to review said memories to compare against added information to draw conclusions. Then you have people like the Holmes bros who see something seemingly innocuous and file it away then immediately make a connection when new information is presented to them.
Personally, I am above average in intelligence with an exceptional memory and honestly it kind of sucks, especially now that it is starting to fade with age finally. Remembering every single mistake or bad experience with total clarity is grueling. And now I am losing the benefits that came with it to age. But at my peak when I participated in some tests and studies back in my college to 30s years, yeah I could rewind back to a previous thing I had experienced and visualize all the details with sharp clarity. Not to the degree portrayed in fiction of course, but well enough that I remember every phone number I have ever had in my life, have vivid memories of things that happened as far back as when I was five, and can recite written passages, faces and names of hundreds of casual acquaintances from over the years, and a bunch of other completely useless trivial shit I wish my head was not crammed with. And if you don't have this degree of memory, it in no way implies you are stupid just that your brain is more efficient at filtering out irrelevant data. And probably not spending every night in bed doing a complete review of the prior day instead of getting enough rest.
Having said all that shit, human brains are fucked up enough with their heuristic shortcuts, perception bias, and basic chemical analog nature that I would never every trust human memory as a single source of evidentiary truth under any circumstances. And with where AI is headed, I can't say I have much faith in electronic memory anymore either.
en.wikipedia.org