A "mistaken belief" refers to thinking or believing something that is not true or accurate. It means that a person has misunderstood or misinterpreted a situation, idea, or fact and holds an incorrect belief about it. Full definition
There are a lot of mistaken beliefs in how to find a healthy good dog from a breeder. (dogplay.com)
The issue of mistaken belief about an individual's age as it relates to sexual offences against minors has been readily debated, and not just amongst the legal community. (calgarydefence.com)
Their other mistaken belief: They might only need these «medicines» for a month or two to get over whatever serious symptoms that brought them to me. (stayhealthyandwell.com)