I'm not mistaken.
The original question was why did the ACLU charge the parents to take the case. The ACLU did not charge the parents to take the case. They did it pro bono. Now if they can get paid by the losers after the case that's their business. But the the ACLU lawyers worked pro bono in the first place.
You're parsing your words. Services rendered in the expectation of payment are not rendered pro bono.