It is a legend. Legends typically contain a small sliver of truth, but they become misconstrued and distorted over time.
"A legend contains some facts and becomes exaggerated to the point that real people or events take on a 'larger than life' quality. In contrast, a myth isn't based on fact, but is symbolic storytelling that was never based on fact."
- Bismarck Tribune, "Examining the difference between myths and legends"
"... It was an epoch-defining moment in their distant past. As the historical sources - Herodotus and Eratosthenes - show, it was generally assumed to have been a real event."
- BBC Culture, "Did the Trojan War actually happen?"