He was unmasked because he was going to be in a position to know
1) What happened
2) Who was involved
3) What they did
All of that is true. McCarthy suggest in the article there was plenty of material from other sources that could have been exposed without taking the steps to unmask his name.
It could be O'Bastard's crew just took the scatter gun approach and unmasked hundreds of people as a matter of routine, then figure out what to do with the data later, as needed.