Low intelligence? That's your only theory?

Mate, I've met lawyers who sent millions to Nigeria. They're not low intelligence. They're very smart people.

Who were very desperate and clung to a highly irrational hope because they really needed one. Also, they often believed that it couldn't be a scam, because they were intelligent, and only dumb people get scammed. Quod Erat Demostrandum...

Now, were they low wisdom? Definitely.

The old joke that "intelligence is knowing that a tomato is a fruit, wisdom is not putting it in a fruit salad", is still very true.

Plenty of intelligent people do very dumb things all the time. Nexium, Scientology, a guru's cult who may or may not commit biological attacks at local salad bars. All have intelligent people involved.

After all, they couldn't have cultured their salmonella if they didn't.

Depending on how you read the sentence, it may mean that they will not call you about that specific email, but they will call you if you're being targeted by criminals. So the caller says "I'm not calling you about a specific email that you're received, but because your account is being targeted by criminals".

It's not about having low intelligence. It's about being caught off guard. Not everyone is in a big city and have constant contact with fraudsters. Some people are in small towns where they trust everyone and when they receive a call from the supermarket or some other place they usually just trust them too. So, they are not attempting to find all the flaws in their reasoning, they may just think that the wording was a bit off, but an understandable mistake and continue the conversation.