That's not the reason. The question seems clear to me. Moreover, your assertion could only be true if people believed that more than half of female bank tellers are involved in the feminist movement, which is implausible.
The question most certainly did not seem clear to me. And the assertion does not require more than half of female bank tellers to be involved in the feminist movement.
Rather, bank teller becomes an irrelevant side-fact, and the focus of discussion becomes whether Linda is more likely to be part of the feminist movement given her being deeply concerned with issues of discrimination and social justice.
Human language is imprecise, and comes with assumptions based on context and culture. The people who came up with this question succumbed to the false assumption that the majority of people would interpret the wording of the question the same way they did.
Because of the flawed nature of the question an the incorrect assumptions of the test givers, this question cannot be relied upon to give any measure of the "conjunction fallacy".
