This question received two spam/abusive answers from the same new user, and was automatically protected. As far as I understand the system, it should not have been automatically protected since the two answers were posted by the same user, but it was.
According to the protection FAQ, a question is automatically protected if the number of deleted answers from new users, plus the number of deleted answers with helpful spam flags, equals 3 or higher, with spam answers from new users counted twice. Also, subsequent answers posted by the same user are ignored when evaluating the criteria. As such, the first answer counts as 2 since it's a spam answer from a new user, while the second should count as 0 since it's from the same user.
After researching this, I believe that the bug lies in the fact that the answerer's account is deleted. There have been bugs in the past where the system hasn't handled checking for the same user correctly if the account has been deleted. If this is the case, the likely direct cause of the automatic protection was the fact that the first answer was deleted, then the account was deleted, then the second answer was deleted. I don't know what fully happened, though.
What happened in this case, where two answers from the same user resulted in automatic protection, while this case is clearly excluded usually?
Update: As per animuson's comment, the account was alive and not deleted at the time the spam answer deletions took place; only afterwards was it deleted. So it's not an issue with properly accounting for deleted users.
Per the protection FAQ, the first answer should have counted as 2 toward the check as a deleted answer from a new user with helpful spam flags, then the second should have counted as 0 since it was posted by the same user.
I believe that the cause of the issue is that while the "deleted answers from new users" check does properly exclude answers from the same author, the "deleted answers with helpful spam flags" check does not, and so that answer counted as 1 instead, bringing the sum total up to the necessary 3 for automatic protection. This explanation may not be correct, however, since this question wasn't automatically protected despite having three deleted answers from two different new users, of which at least one has helpful spam flags. (Or it could be a recently introduced bug.)