I’ll have to disagree with you on this point - Toyotomi Hideyoshi, one of the great daimyo unifiers, was born a peasant. While he was unable to assume the role of Taiko due to his blood line - he was never the less samurai. Ironically he implemented many of the policies which cut off future generations from making this transition during the Tokugawa period. Even then there were rare occurences.
I will agree that they should not have used the term Samurai in their descriptions.
“As the power of these regional clans grew, their chief was typically a distant relative of the emperor, and a lesser member of either the Fujiwara, Minamoto, or Taira clans.”