It appears that in the rush to be dramatic, the Washington Post got their facts wrong.
Here's a quote from the corrected story and the mea cupla at the end of the article.
The OP gave a sufficient quote for me to make a response without having to read the story. It's only because the Washington Post initially got the story wrong, that reading it became necessary.
Reading the story, it appears the group was planning on making a last minute publicity dump of 50,000 registrations at the last moment to file them. At least we now have our answer to the question posed in another thread on why some states require registration well in advance of election day. There's no way Indiana election officials could handle 50,000 registrations dumped on them the day before.
Incidentally, that arbitrary goal likely was a good part of the problem, much like the goals for new accounts for Wells Fargo employees proved a problem. Trying to meet that goal created incentives to be less than worried that complete and accurate registrations were submitted, and may have encouraged some to create applications that they knew would be rejected.