The second text uses disinterested in its traditional sense: unbiased or impartial.
Bonnie is excellent in her position as class treasurer. She always manages to be disinterested in student council debates about the allocation of extracurricular funds.
The first text uses disinterested in its nontraditional sense: uninterested or indifferent.
Bonnie is happy with her position as class treasurer. Though she would have the support of the student council, she is disinterested in running for student body president.
Most style guides recommend to use the traditional sense of the word disinterested because it is considered more standard.
Which text uses the word disinterested in its traditional sense?
A: Bonnie is excellent in her position as class treasurer. She always manages to be disinterested in student council debates about the allocation of extracurricular funds.
B: Bonnie is happy with her position as class treasurer. Though she would have the support of the student council, she is disinterested in running for student body president.